diff --git a/CMakeLists.txt b/CMakeLists.txt
index a8402f3d5..8e90061db 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -14,15 +14,21 @@ project(
   VERSION 0.1.0
 )
 
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED True)
+
 string(TIMESTAMP BUILD_TIMESTAMP "%Y.%m.%d" UTC)
 add_compile_definitions(OBSIDIAN_TIMESTAMP="${BUILD_TIMESTAMP}")
-
 if(CONSOLE_ONLY)
-  add_compile_definitions(CONSOLE_ONLY=1)
+  add_compile_definitions(CONSOLE_ONLY)
+endif()
+if(WIN32)
+  add_compile_definitions(WIN32_LEAN_AND_MEAN)
+  add_compile_definitions(UNICODE)
+  add_compile_definitions(_UNICODE)
+elseif(NOT APPLE AND NOT CONSOLE_ONLY)
+  add_compile_definitions(USE_XFT)
 endif()
-
-set(CMAKE_CXX_STANDARD 17)
-set(CMAKE_CXX_STANDARD_REQUIRED True)
 if(MSVC)
   # get the number of logical cores for parallel build
   cmake_host_system_information(RESULT LOGICAL_CORES QUERY NUMBER_OF_LOGICAL_CORES)
diff --git a/source/bsp.cc b/source/bsp.cc
index 98bb162a5..a4e34bba3 100644
--- a/source/bsp.cc
+++ b/source/bsp.cc
@@ -218,7 +218,7 @@ bool ValidateMapName(char *name)
     // Ok, convert to upper case
     for (char *s = name; *s; s++)
     {
-        *s = toupper(*s);
+        *s = ToUpperASCII(*s);
     }
 
     return true;
diff --git a/source/bsp_wad.cc b/source/bsp_wad.cc
index 03d8c397f..060819499 100644
--- a/source/bsp_wad.cc
+++ b/source/bsp_wad.cc
@@ -648,7 +648,7 @@ static bool IsDummyMarker(const char *name)
     if (strlen(name) < 3)
         return false;
 
-    if (!strchr("PSF", toupper(name[0])))
+    if (!strchr("PSF", ToUpperASCII(name[0])))
         return false;
 
     if (!isdigit(name[1]))
diff --git a/source/csg_bsp.cc b/source/csg_bsp.cc
index a4693741f..13f7df14c 100644
--- a/source/csg_bsp.cc
+++ b/source/csg_bsp.cc
@@ -28,10 +28,10 @@
 #include "hdr_fltk.h"
 #endif
 #include "hdr_lua.h"
-#include "headers.h"
 #include "lib_util.h"
 #include "m_lua.h"
 #include "main.h"
+#include "sys_assert.h"
 #include "sys_macro.h"
 
 double QUANTIZE_GRID;
diff --git a/source/csg_doom.cc b/source/csg_doom.cc
index 4c2e977bc..bc16d93e6 100644
--- a/source/csg_doom.cc
+++ b/source/csg_doom.cc
@@ -29,9 +29,9 @@
 #include "hdr_fltk.h"
 #include "hdr_ui.h" // ui_build.h
 #endif
-#include "headers.h"
 #include "lib_util.h"
 #include "main.h"
+#include "sys_assert.h"
 #include "sys_macro.h"
 
 // Properties
@@ -841,8 +841,8 @@ template <> struct hash<Doom::vertex_map_key_s>
     size_t operator()(const Doom::vertex_map_key_s &k) const
     {
         size_t h = 0;
-        h ^= std::hash<int>()(k.x);
-        h ^= std::hash<int>()(k.y);
+        h ^= IntHash(k.x);
+        h ^= IntHash(k.y);
         return h;
     }
 };
@@ -3168,7 +3168,6 @@ static void WriteFraggleScript()
 
 void FreeStuff()
 {
-    // This is erroring out right now
     std::for_each(vertices.begin(), vertices.end(), [](auto *i) { delete i; });
     std::for_each(linedefs.begin(), linedefs.end(), [](auto *i) { delete i; });
     std::for_each(sidedefs.begin(), sidedefs.end(), [](auto *i) { delete i; });
diff --git a/source/csg_main.cc b/source/csg_main.cc
index a3c52f8cf..d4d28c0b9 100644
--- a/source/csg_main.cc
+++ b/source/csg_main.cc
@@ -28,10 +28,11 @@
 #include "hdr_fltk.h"
 #endif
 #include "hdr_lua.h"
-#include "headers.h"
 #include "lib_util.h"
 #include "m_lua.h"
 #include "main.h"
+#include "sys_assert.h"
+#include "sys_macro.h"
 
 #define EPSILON 0.001
 
diff --git a/source/csg_shade.cc b/source/csg_shade.cc
index 99591b225..99aaecf94 100644
--- a/source/csg_shade.cc
+++ b/source/csg_shade.cc
@@ -28,10 +28,10 @@
 #include "hdr_ui.h"
 #endif
 #include "hdr_lua.h"
-#include "headers.h"
 #include "lib_argv.h"
 #include "lib_util.h"
 #include "main.h"
+#include "sys_macro.h"
 
 /*
 
diff --git a/source/csg_spots.cc b/source/csg_spots.cc
index 0e43873ec..ae144c945 100644
--- a/source/csg_spots.cc
+++ b/source/csg_spots.cc
@@ -20,14 +20,11 @@
 //----------------------------------------------------------------------
 
 #include "hdr_lua.h"
-#include "headers.h"
 #include "lib_argv.h"
 #include "lib_util.h"
 #include "main.h"
-
-#ifdef WIN32
-#include <iso646.h>
-#endif
+#include "sys_assert.h"
+#include "sys_macro.h"
 
 #define GRID_SIZE 20
 
@@ -311,7 +308,7 @@ static void remove_dud_cells()
 
 static bool test_mon_area(int x1, int y1, int x2, int y2, int want)
 {
-    if (x1 < 0 or x2 >= grid_W or y1 < 0 or y2 >= grid_H)
+    if (x1 < 0 || x2 >= grid_W || y1 < 0 || y2 >= grid_H)
     {
         return false;
     }
diff --git a/source/dm_extra.cc b/source/dm_extra.cc
index 73bcd21a5..336f1e796 100644
--- a/source/dm_extra.cc
+++ b/source/dm_extra.cc
@@ -26,7 +26,6 @@
 #include "hdr_ui.h"
 #endif
 #include "hdr_lua.h"
-#include "headers.h"
 #include "images.h"
 #include "lib_tga.h"
 #include "lib_util.h"
@@ -35,6 +34,9 @@
 #include "m_lua.h"
 #include "main.h"
 #include "physfs.h"
+#include "sys_assert.h"
+#include "sys_endian.h"
+#include "sys_macro.h"
 #include "tx_forge.h"
 #include "tx_skies.h"
 
@@ -656,7 +658,7 @@ int fsky_add_hills(lua_State *L)
 
 static int FontIndexForChar(char ch)
 {
-    ch = toupper(ch);
+    ch = ToUpperASCII(ch);
 
     if (ch == ' ')
     {
diff --git a/source/dm_prefab.cc b/source/dm_prefab.cc
index 2e6a4d690..72fd9e579 100644
--- a/source/dm_prefab.cc
+++ b/source/dm_prefab.cc
@@ -66,12 +66,13 @@
 #include "hdr_ui.h"
 #endif
 #include "hdr_lua.h"
-#include "headers.h"
 #include "lib_util.h"
 #include "lib_wad.h"
 #include "m_lua.h"
 #include "main.h"
 #include "physfs.h"
+#include "sys_assert.h"
+#include "sys_macro.h"
 
 // callbacks for AJ-Polygonator
 
diff --git a/source/g_doom.cc b/source/g_doom.cc
index 325a0c91f..be8f3b687 100644
--- a/source/g_doom.cc
+++ b/source/g_doom.cc
@@ -24,8 +24,6 @@
 #include <bitset>
 #include <string>
 
-#include "headers.h"
-
 #ifndef CONSOLE_ONLY
 #include "hdr_fltk.h"
 #endif
@@ -35,13 +33,13 @@
 #include "lib_zip.h"
 #include "m_cookie.h"
 #include "m_lua.h"
+#include "m_trans.h"
 #include "main.h"
+#include "sys_assert.h"
+#include "sys_endian.h"
+#include "sys_macro.h"
 #include "sys_xoshiro.h"
 
-#ifdef WIN32
-#include <iso646.h>
-#endif
-
 #include "bsp.h"
 
 // SLUMP for Vanilla Doom
@@ -445,7 +443,7 @@ static void WriteBehavior()
     /*raw_behavior_header_t behavior;
 
     std::string_view acs{"ACS"};
-    std::copy(acs.data(), acs.data() + 4, behavior.marker);
+    memcpy(behavior.marker, acs.data(), 4);
 
     behavior.offset = LE_U32(8);
     behavior.func_num = 0;
@@ -573,7 +571,7 @@ static void FreeLumps()
 {
     delete header_lump;
     header_lump = nullptr;
-    if (not UDMF_mode)
+    if (!UDMF_mode)
     {
         delete thing_lump;
         thing_lump = nullptr;
@@ -601,7 +599,7 @@ void Doom::BeginLevel()
     FreeLumps();
 
     header_lump = new qLump_c();
-    if (not UDMF_mode)
+    if (!UDMF_mode)
     {
         thing_lump   = new qLump_c();
         vertex_lump  = new qLump_c();
@@ -658,7 +656,7 @@ void Doom::EndLevel(std::string level_name)
         WriteLump("TEXTMAP", textmap_lump);
     }
 
-    if (not UDMF_mode)
+    if (!UDMF_mode)
     {
         WriteLump("THINGS", thing_lump);
         WriteLump("LINEDEFS", linedef_lump);
@@ -737,7 +735,7 @@ void Doom::AddVertex(int x, int y)
         y += 32;
     }
 
-    if (not UDMF_mode)
+    if (!UDMF_mode)
     {
         raw_vertex_t vert;
 
@@ -765,15 +763,15 @@ int Doom::v094_add_vertex(lua_State *L)
 
 void Doom::AddSector(int f_h, std::string f_tex, int c_h, std::string c_tex, int light, int special, int tag)
 {
-    if (not UDMF_mode)
+    if (!UDMF_mode)
     {
         raw_sector_t sec;
 
         sec.floor_h = LE_S16(f_h);
         sec.ceil_h  = LE_S16(c_h);
 
-        std::copy(f_tex.data(), f_tex.data() + 8, sec.floor_tex);
-        std::copy(c_tex.data(), c_tex.data() + 8, sec.ceil_tex);
+        memcpy(sec.floor_tex, f_tex.data(), 8);
+        memcpy(sec.ceil_tex, c_tex.data(), 8);
 
         sec.light   = LE_U16(light);
         sec.special = LE_U16(special);
@@ -810,15 +808,15 @@ int Doom::v094_add_sector(lua_State *L)
 
 void Doom::AddSidedef(int sector, std::string l_tex, std::string m_tex, std::string u_tex, int x_offset, int y_offset)
 {
-    if (not UDMF_mode)
+    if (!UDMF_mode)
     {
         raw_sidedef_t side;
 
         side.sector = LE_S16(sector);
 
-        std::copy(l_tex.data(), l_tex.data() + 8, side.lower_tex);
-        std::copy(m_tex.data(), m_tex.data() + 8, side.mid_tex);
-        std::copy(u_tex.data(), u_tex.data() + 8, side.upper_tex);
+        memcpy(side.lower_tex, l_tex.data(), 8);
+        memcpy(side.mid_tex, m_tex.data(), 8);
+        memcpy(side.upper_tex, u_tex.data(), 8);
 
         side.x_offset = LE_S16(x_offset);
         side.y_offset = LE_S16(y_offset);
@@ -854,7 +852,7 @@ void Doom::AddLinedef(int vert1, int vert2, int side1, int side2, int type, int
 {
     if (sub_format != SUBFMT_Hexen)
     {
-        if (not UDMF_mode)
+        if (!UDMF_mode)
         {
             raw_linedef_t line;
 
@@ -926,7 +924,7 @@ void Doom::AddLinedef(int vert1, int vert2, int side1, int side2, int type, int
     }
     else // Hexen format
     {
-        if (not UDMF_mode)
+        if (!UDMF_mode)
         {
             raw_hexen_linedef_t line;
 
@@ -946,7 +944,7 @@ void Doom::AddLinedef(int vert1, int vert2, int side1, int side2, int type, int
 
             if (args)
             {
-                std::copy(args, args + 5, line.args);
+                memcpy(line.args, args, 5);
             }
 
             linedef_lump->Append(&line, sizeof(line));
@@ -1109,7 +1107,7 @@ void Doom::AddThing(int x, int y, int h, int type, int angle, int options, int t
 
     if (sub_format != SUBFMT_Hexen)
     {
-        if (not UDMF_mode)
+        if (!UDMF_mode)
         {
             raw_thing_t thing;
 
@@ -1186,7 +1184,7 @@ void Doom::AddThing(int x, int y, int h, int type, int angle, int options, int t
     }
     else // Hexen format
     {
-        if (not UDMF_mode)
+        if (!UDMF_mode)
         {
             raw_hexen_thing_t thing;
 
@@ -1213,7 +1211,7 @@ void Doom::AddThing(int x, int y, int h, int type, int angle, int options, int t
 
             if (args)
             {
-                std::copy(args, args + 5, thing.args);
+                memcpy(thing.args, args, 5);
             }
 
             thing_lump->Append(&thing, sizeof(thing));
@@ -1315,7 +1313,7 @@ int Doom::v094_add_thing(lua_State *L)
 
 int Doom::NumVertexes()
 {
-    if (not UDMF_mode)
+    if (!UDMF_mode)
     {
         return vertex_lump->GetSize() / sizeof(raw_vertex_t);
     }
@@ -1324,7 +1322,7 @@ int Doom::NumVertexes()
 
 int Doom::NumSectors()
 {
-    if (not UDMF_mode)
+    if (!UDMF_mode)
     {
         return sector_lump->GetSize() / sizeof(raw_sector_t);
     }
@@ -1333,7 +1331,7 @@ int Doom::NumSectors()
 
 int Doom::NumSidedefs()
 {
-    if (not UDMF_mode)
+    if (!UDMF_mode)
     {
         return sidedef_lump->GetSize() / sizeof(raw_sidedef_t);
     }
@@ -1342,7 +1340,7 @@ int Doom::NumSidedefs()
 
 int Doom::NumLinedefs()
 {
-    if (not UDMF_mode)
+    if (!UDMF_mode)
     {
         if (sub_format == SUBFMT_Hexen)
         {
@@ -1356,7 +1354,7 @@ int Doom::NumLinedefs()
 
 int Doom::NumThings()
 {
-    if (not UDMF_mode)
+    if (!UDMF_mode)
     {
         if (sub_format == SUBFMT_Hexen)
         {
@@ -1529,17 +1527,7 @@ bool Doom::game_interface_c::Start(const char *preset)
     if (map_format == FORMAT_UDMF)
     {
         UDMF_mode = true;
-#ifdef __APPLE__
-        setlocale(LC_NUMERIC, "C");
-#elif __unix__
-#ifndef __linux__
         setlocale(LC_NUMERIC, "C");
-#else
-        std::setlocale(LC_NUMERIC, "C");
-#endif
-#else
-        std::setlocale(LC_NUMERIC, "C");
-#endif
     }
     else
     {
@@ -1563,17 +1551,7 @@ bool Doom::game_interface_c::Finish(bool build_ok)
 
     if (UDMF_mode)
     {
-#ifdef __APPLE__
-        setlocale(LC_NUMERIC, numeric_locale.c_str());
-#elif __unix__
-#ifndef __linux__
         setlocale(LC_NUMERIC, numeric_locale.c_str());
-#else
-        std::setlocale(LC_NUMERIC, numeric_locale.c_str());
-#endif
-#else
-        std::setlocale(LC_NUMERIC, numeric_locale.c_str());
-#endif
     }
 
     if (build_ok)
diff --git a/source/g_wolf.cc b/source/g_wolf.cc
index d05529b83..417ee40f1 100644
--- a/source/g_wolf.cc
+++ b/source/g_wolf.cc
@@ -23,10 +23,11 @@
 #include "hdr_ui.h"
 #endif
 #include "hdr_lua.h"
-#include "headers.h"
 #include "lib_util.h"
 #include "m_lua.h"
+#include "m_trans.h"
 #include "main.h"
+#include "sys_assert.h"
 
 #define TEMP_GAMEFILE "GAMEMAPS.TMP"
 #define TEMP_MAPTEMP  "MAPTEMP.TMP"
diff --git a/source/headers.h b/source/headers.h
deleted file mode 100644
index ae0b4c4a5..000000000
--- a/source/headers.h
+++ /dev/null
@@ -1,79 +0,0 @@
-//------------------------------------------------------------------------
-//  INCLUDES
-//------------------------------------------------------------------------
-//
-//  OBSIDIAN Level Maker
-//
-//  Copyright (C) 2021-2022 The OBSIDIAN Team
-//  Copyright (C) 2006-2017 Andrew Apted
-//
-//  This program is free software; you can redistribute it and/or
-//  modify it under the terms of the GNU General Public License
-//  as published by the Free Software Foundation; either version 2
-//  of the License, or (at your option) any later version.
-//
-//  This program is distributed in the hope that it will be useful,
-//  but WITHOUT ANY WARRANTY; without even the implied warranty of
-//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-//  GNU General Public License for more details.
-//
-//------------------------------------------------------------------------
-
-#pragma once
-
-// we C++
-#ifdef NULL
-#undef NULL
-#endif
-#define NULL nullptr
-
-/* OS specifics */
-#ifdef _WIN32
-#define WIN32_LEAN_AND_MEAN
-#include <windows.h>
-#else
-#ifndef CONSOLE_ONLY
-#ifndef __APPLE__
-#include <fontconfig/fontconfig.h>
-#define USE_XFT 1
-#endif
-#endif
-#endif
-
-/* C library */
-
-#include <ctype.h>
-#include <errno.h>
-#include <limits.h>
-#include <math.h>
-#include <stdarg.h>
-#include <stdint.h>
-#include <stdlib.h>
-#include <string.h>
-#include <time.h>
-
-#include <cstdio>
-
-/* STL goodies */
-
-#include <list>
-#include <map>
-#include <string>
-#include <vector>
-
-/* Our own system defs */
-
-#include "sys_assert.h"
-#include "sys_debug.h"
-#include "sys_endian.h"
-#include "sys_macro.h"
-
-/* Internationalization / Localization */
-
-#define _(s)  ob_gettext(s)
-#define N_(s) (s)
-
-const char *ob_gettext(const char *s);
-
-//--- editor settings ---
-// vi:ts=4:sw=4:noexpandtab
diff --git a/source/images.h b/source/images.h
index 6cccc8b33..3e80fefbc 100644
--- a/source/images.h
+++ b/source/images.h
@@ -2,8 +2,6 @@
 
 #pragma once
 
-#include "headers.h"
-
 #ifndef WIN32
 static const char *obsidian_icon[] = {
     "64 64 928 2",
diff --git a/source/lib_argv.cc b/source/lib_argv.cc
index 828699edd..6870bd1f9 100644
--- a/source/lib_argv.cc
+++ b/source/lib_argv.cc
@@ -21,14 +21,15 @@
 
 #include "lib_argv.h"
 
-#include "headers.h"
-#include "lib_util.h"
-
 #ifdef _WIN32
+#include <windows.h>
 #include <processenv.h>
 #include <shellapi.h>
 #endif
 
+#include "lib_util.h"
+#include "sys_assert.h"
+
 std::vector<std::string> argv::list;
 std::unordered_set<char> argv::short_flags;
 
@@ -56,7 +57,7 @@ static void Parse_LongArg(std::string_view arg)
 
 static void Parse_ShortArgs(std::string_view arg)
 {
-    for (std::size_t i = 1; i < arg.size(); ++i)
+    for (size_t i = 1; i < arg.size(); ++i)
     {
         char ch = arg[i];
 
@@ -210,7 +211,7 @@ int argv::Find(const char shortName, const char *longName, int *numParams)
 
         const std::string &str = list[p];
 
-        if (shortName && (shortName == tolower(str[1])) && str[2] == 0)
+        if (shortName && (shortName == ToLowerASCII(str[1])) && str[2] == 0)
         {
             break;
         }
@@ -244,7 +245,7 @@ int argv::Find(const char shortName, const char *longName, int *numParams)
 
 bool argv::IsOption(const int index)
 {
-    return list.at(index)[0] == '-';
+    return list[index][0] == '-';
 }
 
 //--- editor settings ---
diff --git a/source/lib_parse.cc b/source/lib_parse.cc
index fdc9e4c89..8464da0a8 100644
--- a/source/lib_parse.cc
+++ b/source/lib_parse.cc
@@ -18,9 +18,11 @@
 
 #include "lib_parse.h"
 
-#include <cassert>
-#include <cctype>
-#include <cstdlib>
+#include <ctype.h>
+#include <stdlib.h>
+
+#include "lib_util.h"
+#include "sys_assert.h"
 
 namespace ajparse
 {
@@ -39,10 +41,10 @@ token_kind_e lexer_c::Next(std::string &s)
     if (ch == '"')
         return ParseString(s);
 
-    if (ch == '-' || ch == '+' || std::isdigit(ch))
+    if (ch == '-' || ch == '+' || IsDigitASCII(ch))
         return ParseNumber(s);
 
-    if (std::isalpha(ch) || ch == '_' || ch >= 128)
+    if (IsAlphaASCII(ch) || ch == '_' || ch >= 128)
         return ParseIdentifier(s);
 
     // anything else is a single-character symbol
@@ -53,10 +55,10 @@ token_kind_e lexer_c::Next(std::string &s)
 
 bool lexer_c::Match(const char *s)
 {
-    assert(s);
-    assert(s[0]);
+    SYS_ASSERT(s);
+    SYS_ASSERT(s[0]);
 
-    bool is_keyword = std::isalnum(s[0]);
+    bool is_keyword = IsAlphanumericASCII(s[0]);
 
     SkipToNext();
 
@@ -72,9 +74,9 @@ bool lexer_c::Match(const char *s)
 
         // don't change a char when high-bit is set (for UTF-8)
         if (A < 128)
-            A = std::tolower(A);
+            A = ToLowerASCII(A);
         if (B < 128)
-            B = std::tolower(B);
+            B = ToLowerASCII(B);
 
         if (A != B)
             return false;
@@ -87,7 +89,7 @@ bool lexer_c::Match(const char *s)
     {
         unsigned char ch = (unsigned char)data[pos];
 
-        if (std::isalnum(ch) || ch >= 128)
+        if (IsAlphanumericASCII(ch) || ch >= 128)
             return false;
     }
 
@@ -108,13 +110,13 @@ void lexer_c::Rewind()
 int LEX_Int(const std::string &s)
 {
     // strtol handles all the integer sequences of the UDMF spec
-    return (int)std::strtol(s.c_str(), NULL, 0);
+    return (int)strtol(s.c_str(), NULL, 0);
 }
 
 double LEX_Double(const std::string &s)
 {
     // strtod handles all the floating-point sequences of the UDMF spec
-    return std::strtod(s.c_str(), NULL);
+    return strtod(s.c_str(), NULL);
 }
 
 bool LEX_Boolean(const std::string &s)
@@ -195,16 +197,16 @@ token_kind_e lexer_c::ParseIdentifier(std::string &s)
 
         // don't change a char when high-bit is set (for UTF-8)
         if (ch < 128)
-            ch = std::tolower(ch);
+            ch = ToLowerASCII(ch);
 
-        if (!(std::isalnum(ch) || ch == '_' || ch >= 128))
+        if (!(IsAlphanumericASCII(ch) || ch == '_' || ch >= 128))
             break;
 
         s.push_back((char)ch);
         pos++;
     }
 
-    assert(s.size() > 0);
+    SYS_ASSERT(s.size() > 0);
 
     return TOK_Ident;
 }
@@ -214,7 +216,7 @@ token_kind_e lexer_c::ParseNumber(std::string &s)
     if (data[pos] == '-' || data[pos] == '+')
     {
         // no digits after the sign?
-        if (pos + 1 >= data.size() || !std::isdigit(data[pos + 1]))
+        if (pos + 1 >= data.size() || !IsDigitASCII(data[pos + 1]))
         {
             s.push_back(data[pos++]);
             return TOK_Symbol;
@@ -231,7 +233,7 @@ token_kind_e lexer_c::ParseNumber(std::string &s)
         unsigned char ch = (unsigned char)data[pos];
 
         // this is fairly lax, but adequate for our purposes
-        if (!(std::isalnum(ch) || ch == '+' || ch == '-' || ch == '.'))
+        if (!(IsAlphanumericASCII(ch) || ch == '+' || ch == '-' || ch == '.'))
             break;
     }
 
@@ -328,14 +330,14 @@ void lexer_c::ParseEscape(std::string &s)
         *p++ = '0';
 
         ch = (unsigned char)data[pos];
-        if (std::isxdigit(ch))
+        if (IsXDigitASCII(ch))
         {
             *p++ = ch;
             pos++;
         }
 
         ch = (unsigned char)data[pos];
-        if (std::isxdigit(ch))
+        if (IsXDigitASCII(ch))
         {
             *p++ = ch;
             pos++;
@@ -343,7 +345,7 @@ void lexer_c::ParseEscape(std::string &s)
 
         *p = 0;
 
-        int val = (int)std::strtol(buffer, NULL, 0);
+        int val = (int)strtol(buffer, NULL, 0);
         s.push_back((char)val);
         return;
     }
diff --git a/source/lib_tga.cc b/source/lib_tga.cc
index 18e3b550e..d0f6d2c27 100644
--- a/source/lib_tga.cc
+++ b/source/lib_tga.cc
@@ -26,7 +26,6 @@
 
 #include "lib_tga.h"
 
-#include "headers.h"
 #include "m_addons.h"
 #include "main.h"
 
diff --git a/source/lib_util.cc b/source/lib_util.cc
index 119427efe..c072157f9 100644
--- a/source/lib_util.cc
+++ b/source/lib_util.cc
@@ -21,11 +21,6 @@
 
 #include "lib_util.h"
 
-#include <chrono>
-
-#include "grapheme.h"
-#include "headers.h"
-#include "main.h"
 #ifndef _WIN32
 #include <dirent.h>
 #include <ftw.h>
@@ -36,6 +31,12 @@
 #ifdef __MINGW32__
 #include <sys/stat.h>
 #endif
+#include <chrono>
+
+#include "grapheme.h"
+#include "main.h"
+#include "sys_assert.h"
+#include "sys_macro.h"
 
 #ifdef _WIN32                                   // Windows API
 static inline bool IsDirectorySeparator(const char c)
@@ -742,7 +743,7 @@ uint64_t StringHash64(const std::string &str)
         }
         for (size_t c = str.size() - 1; c > 0; c--)
         {
-            hash2 = (hash2 << 5) - hash2 + str.at(c);
+            hash2 = (hash2 << 5) - hash2 + str[c];
         }
     }
 
diff --git a/source/lib_wad.cc b/source/lib_wad.cc
index 01f8b58d1..c3d7c9c3c 100644
--- a/source/lib_wad.cc
+++ b/source/lib_wad.cc
@@ -23,10 +23,11 @@
 
 #include <list>
 
-#include "headers.h"
 #include "lib_util.h"
 #include "main.h"
 #include "physfs.h"
+#include "sys_assert.h"
+#include "sys_endian.h"
 
 // #define LogPrintf  printf
 
@@ -275,7 +276,7 @@ void WAD_NewLump(std::string name)
 
     memset(&wad_W_lump, 0, sizeof(wad_W_lump));
 
-    std::copy(name.data(), name.data() + name.size(), wad_W_lump.name);
+    memcpy(wad_W_lump.name, name.data(), name.size());
 
     wad_W_lump.start = wad_W_fp.tellp();
 }
diff --git a/source/lib_zip.cc b/source/lib_zip.cc
index c9327703e..3153037f8 100644
--- a/source/lib_zip.cc
+++ b/source/lib_zip.cc
@@ -21,7 +21,6 @@
 
 #include "lib_zip.h"
 
-#include "headers.h"
 #include "lib_util.h"
 #include "miniz.h"
 
diff --git a/source/m_about.cc b/source/m_about.cc
index 53f6d8537..1b7bfd1bb 100644
--- a/source/m_about.cc
+++ b/source/m_about.cc
@@ -21,9 +21,10 @@
 
 #include "hdr_fltk.h"
 #include "hdr_ui.h"
-#include "headers.h"
 #include "lib_util.h"
+#include "m_trans.h"
 #include "main.h"
+#include "sys_assert.h"
 
 class UI_About : public Fl_Window
 {
diff --git a/source/m_addons.cc b/source/m_addons.cc
index 80f1705d1..7a783dbc5 100644
--- a/source/m_addons.cc
+++ b/source/m_addons.cc
@@ -21,8 +21,6 @@
 
 #include "m_addons.h"
 
-#include "headers.h"
-
 #ifndef CONSOLE_ONLY
 #include "hdr_fltk.h"
 #include "hdr_ui.h"
diff --git a/source/m_addons.h b/source/m_addons.h
index 68acdcd6e..848247eac 100644
--- a/source/m_addons.h
+++ b/source/m_addons.h
@@ -22,8 +22,8 @@
 #pragma once
 
 #include <stdint.h>
+#include <stdio.h>
 
-#include <cstdio>
 #include <fstream>
 #include <map>
 #include <string>
diff --git a/source/m_cookie.cc b/source/m_cookie.cc
index e2858362d..3b6015884 100644
--- a/source/m_cookie.cc
+++ b/source/m_cookie.cc
@@ -28,11 +28,11 @@
 #include "hdr_ui.h"
 #endif
 #include "hdr_lua.h"
-#include "headers.h"
 #include "lib_argv.h"
 #include "lib_util.h"
 #include "m_lua.h"
 #include "main.h"
+#include "sys_assert.h"
 
 enum struct cookie_context_e
 {
@@ -85,7 +85,7 @@ static void Cookie_SetValue(std::string name, std::string value)
         {
             try
             {
-                next_rand_seed = std::stoull(value);
+                next_rand_seed = stoull(value);
                 return;
             }
             catch (std::invalid_argument &e)
@@ -124,7 +124,7 @@ static bool Cookie_ParseLine(std::string buf)
         return true;
     }
 
-    while (std::isspace(buf[0]))
+    while (IsSpaceASCII(buf[0]))
     {
         buf.erase(buf.begin());
     }
@@ -137,16 +137,16 @@ static bool Cookie_ParseLine(std::string buf)
 
     std::string::size_type pos = buf.find('=');
 
-    while (pos > 0 && std::isspace(buf[pos - 1]))
+    while (pos > 0 && IsSpaceASCII(buf[pos - 1]))
     {
         buf.erase(buf.begin() + (pos - 1));
         pos--;
     }
-    while (pos + 1 < buf.size() && std::isspace(buf[pos + 1]))
+    while (pos + 1 < buf.size() && IsSpaceASCII(buf[pos + 1]))
     {
         buf.erase(buf.begin() + (pos + 1));
     }
-    while (std::isspace(buf[buf.size() - 1]))
+    while (IsSpaceASCII(buf[buf.size() - 1]))
     {
         buf.erase(buf.end() - 1);
     }
@@ -174,17 +174,7 @@ bool Cookie_Load(std::string filename)
 
     active_module.clear();
 
-#ifdef __APPLE__
     setlocale(LC_NUMERIC, "C");
-#elif __unix__
-#ifndef __linux__
-    setlocale(LC_NUMERIC, "C");
-#else
-    std::setlocale(LC_NUMERIC, "C");
-#endif
-#else
-    std::setlocale(LC_NUMERIC, "C");
-#endif
     std::ifstream cookie_fp(filename, std::ios::in);
 
     if (!cookie_fp.is_open())
@@ -218,17 +208,7 @@ bool Cookie_Load(std::string filename)
             LogPrintf("DONE.\n\n");
         }
     }
-#ifdef __APPLE__
     setlocale(LC_NUMERIC, numeric_locale.c_str());
-#elif __unix__
-#ifndef __linux__
-    setlocale(LC_NUMERIC, numeric_locale.c_str());
-#else
-    std::setlocale(LC_NUMERIC, numeric_locale.c_str());
-#endif
-#else
-    std::setlocale(LC_NUMERIC, numeric_locale.c_str());
-#endif
     return true;
 }
 
@@ -260,17 +240,7 @@ bool Cookie_LoadString(std::string str, bool _keep_seed)
 bool Cookie_Save(std::string filename)
 {
     context = cookie_context_e::Save;
-#ifdef __APPLE__
     setlocale(LC_NUMERIC, "C");
-#elif __unix__
-#ifndef __linux__
-    setlocale(LC_NUMERIC, "C");
-#else
-    std::setlocale(LC_NUMERIC, "C");
-#endif
-#else
-    std::setlocale(LC_NUMERIC, "C");
-#endif
     std::ofstream cookie_fp(filename, std::ios::out);
 
     if (!cookie_fp.is_open())
@@ -306,17 +276,7 @@ bool Cookie_Save(std::string filename)
     }
 
     cookie_fp.close();
-#ifdef __APPLE__
     setlocale(LC_NUMERIC, numeric_locale.c_str());
-#elif __unix__
-#ifndef __linux__
-    setlocale(LC_NUMERIC, numeric_locale.c_str());
-#else
-    std::setlocale(LC_NUMERIC, numeric_locale.c_str());
-#endif
-#else
-    std::setlocale(LC_NUMERIC, numeric_locale.c_str());
-#endif
     return true;
 }
 
diff --git a/source/m_cookie.h b/source/m_cookie.h
index 5651ed0fa..49ee841c3 100644
--- a/source/m_cookie.h
+++ b/source/m_cookie.h
@@ -21,7 +21,8 @@
 
 #pragma once
 
-#include <cstdio>
+#include <stdio.h>
+
 #include <string>
 
 bool Cookie_Load(std::string filename);
diff --git a/source/m_dialog.cc b/source/m_dialog.cc
index 74db7548a..c5fb924c6 100644
--- a/source/m_dialog.cc
+++ b/source/m_dialog.cc
@@ -25,16 +25,14 @@
 #include <limits>
 #include <string>
 
-#ifdef WIN32
-#include <iso646.h>
-#endif
-
 #include "hdr_fltk.h"
 #include "hdr_ui.h"
-#include "headers.h"
 #include "lib_util.h"
 #include "m_lua.h"
+#include "m_trans.h"
 #include "main.h"
+#include "sys_assert.h"
+#include "sys_macro.h"
 
 std::string last_directory;
 
@@ -242,7 +240,7 @@ std::string DLG_OutputFilename(const char *ext, const char *preset)
     // uppercase the first word
     for (char *p = &kind_buf[0]; *p && *p != ' '; p++)
     {
-        *p = toupper(*p);
+        *p = ToUpperASCII(*p);
     }
 
     // save and restore the font height
@@ -344,8 +342,8 @@ void DLG_EditSeed(void)
     {
         for (long unsigned int i = 0; i < word.size(); i++)
         {
-            char character = word.at(i);
-            if (!std::isdigit(character))
+            char character = word[i];
+            if (!IsDigitASCII(character))
             {
                 throw std::runtime_error(
                     // clang-format off
@@ -354,7 +352,7 @@ void DLG_EditSeed(void)
             }
         }
         did_specify_seed = true;
-        next_rand_seed   = std::stoull(word);
+        next_rand_seed   = stoull(word);
         return;
     }
     catch (std::invalid_argument &e)
diff --git a/source/m_lua.cc b/source/m_lua.cc
index 46f997bae..0c2dd94c9 100644
--- a/source/m_lua.cc
+++ b/source/m_lua.cc
@@ -20,24 +20,21 @@
 //----------------------------------------------------------------------
 
 #include <algorithm>
-#ifdef WIN32
-#include <iso646.h>
-#endif
 
 #ifndef CONSOLE_ONLY
 #include "hdr_fltk.h"
 #include "hdr_ui.h"
 #endif
 #include "ff_main.h"
-#include "headers.h"
 #include "lib_util.h"
+#define LUA_IMPL
+#include "m_lua.h"
+#include "m_trans.h"
 #include "main.h"
 #include "physfs.h"
+#include "sys_assert.h"
 #include "sys_xoshiro.h"
 
-#define LUA_IMPL
-#include "m_lua.h"
-
 static lua_State *LUA_ST;
 
 static bool has_loaded        = false;
diff --git a/source/m_manage.cc b/source/m_manage.cc
index 267138ebc..4975c692f 100644
--- a/source/m_manage.cc
+++ b/source/m_manage.cc
@@ -21,11 +21,12 @@
 
 #include "hdr_fltk.h"
 #include "hdr_ui.h"
-#include "headers.h"
 #include "lib_util.h"
 #include "m_cookie.h"
 #include "m_lua.h"
+#include "m_trans.h"
 #include "main.h"
+#include "sys_assert.h"
 
 // forward decls
 class UI_Manage_Config;
diff --git a/source/m_options.cc b/source/m_options.cc
index 8df736792..f6121a140 100644
--- a/source/m_options.cc
+++ b/source/m_options.cc
@@ -23,7 +23,6 @@
 #include "hdr_fltk.h"
 #include "hdr_ui.h"
 #endif
-#include "headers.h"
 #include "lib_argv.h"
 #include "lib_util.h"
 #include "m_addons.h"
diff --git a/source/m_theme.cc b/source/m_theme.cc
index 27ce8b8d7..958fc4213 100644
--- a/source/m_theme.cc
+++ b/source/m_theme.cc
@@ -21,13 +21,14 @@
 
 #include "hdr_fltk.h"
 #include "hdr_ui.h"
-#include "headers.h"
 #include "lib_argv.h"
 #include "lib_util.h"
 #include "m_addons.h"
 #include "m_cookie.h"
 #include "m_trans.h"
 #include "main.h"
+#include "sys_assert.h"
+#include "sys_macro.h"
 
 bool skip_color_picker = false;
 
@@ -597,7 +598,7 @@ class UI_ThemeWin : public Fl_Window
         UI_ThemeWin *that = (UI_ThemeWin *)data;
 
         font_theme = that->opt_font_theme->value();
-        font_style = font_menu_items.at(font_theme).second;
+        font_style = font_menu_items[font_theme].second;
         fl_font(font_style, FL_NORMAL_SIZE);
         fl_message_font(font_style, FL_NORMAL_SIZE);
         main_win->menu_bar->textfont(font_style);
diff --git a/source/m_trans.cc b/source/m_trans.cc
index ac6bdfee2..4d2f842a6 100644
--- a/source/m_trans.cc
+++ b/source/m_trans.cc
@@ -27,15 +27,16 @@
 
 #include "m_trans.h"
 
-#include "hdr_lua.h"
-#include "headers.h"
-#include "lib_util.h"
-#include "main.h"
-
 #ifndef WIN32
 #include <locale.h>
 #endif
 
+#include "hdr_lua.h"
+#include "lib_util.h"
+#include "main.h"
+#include "sys_assert.h"
+#include "sys_macro.h"
+
 //
 // NOTE :
 //    We assume that any string retrieved from our 'trans_store'
@@ -1184,32 +1185,8 @@ void Trans_UnInit()
 
 //----------------------------------------------------------------------
 
-// debugging crud
-std::string mucked_up_string(std::string_view s)
-{
-    std::string buffer;
-    buffer.resize(s.size());
-    int p, q;
-    for (p = s.size() - 1, q = 0; p >= 0 && q < 250; p--, q++)
-    {
-        int ch = s[p];
-        if (ch == '%')
-        {
-            ch = '#';
-        }
-        ch        = (isupper(ch) ? tolower(ch) : toupper(ch));
-        buffer[q] = ch;
-    }
-    buffer[q] = 0;
-    return buffer;
-}
-
 const char *ob_gettext(const char *s)
 {
-#if 0 // DEBUGGING CRUD
-    return mucked_up_string(s);
-#endif
-
     std::map<std::string, std::string>::iterator IT;
 
     IT = trans_store.find(s);
diff --git a/source/m_trans.h b/source/m_trans.h
index 6a9ec5191..f69684c92 100644
--- a/source/m_trans.h
+++ b/source/m_trans.h
@@ -36,5 +36,10 @@ void Trans_UnInit();
 std::string Trans_GetAvailCode(int idx);
 std::string Trans_GetAvailLanguage(int idx);
 
+#define _(s)  ob_gettext(s)
+#define N_(s) (s)
+
+const char *ob_gettext(const char *s);
+
 //--- editor settings ---
 // vi:ts=4:sw=4:noexpandtab
diff --git a/source/main.cc b/source/main.cc
index 18e53f5e9..9cfbaa521 100644
--- a/source/main.cc
+++ b/source/main.cc
@@ -27,7 +27,6 @@
 #include "hdr_fltk.h"
 #include "hdr_ui.h"
 #endif
-#include "headers.h"
 #include "lib_argv.h"
 #include "lib_util.h"
 #include "lib_zip.h"
@@ -863,7 +862,7 @@ void Main::SetupFLTK()
     if (font_theme < num_fonts)
     { // In case the number of installed fonts is
       // reduced between launches
-        font_style = font_menu_items.at(font_theme).second;
+        font_style = font_menu_items[font_theme].second;
     }
     else
     {
@@ -1463,17 +1462,7 @@ hardrestart:;
         debug_messages = true;
     }
 // Grab current numeric locale
-#ifdef __APPLE__
-    numeric_locale = setlocale(LC_NUMERIC, NULL);
-#elif __unix__
-#ifndef __linux__
     numeric_locale = setlocale(LC_NUMERIC, NULL);
-#else
-    numeric_locale = std::setlocale(LC_NUMERIC, NULL);
-#endif
-#else
-    numeric_locale = std::setlocale(LC_NUMERIC, NULL);
-#endif
 
     LogEnableDebug(debug_messages);
 
diff --git a/source/main.h b/source/main.h
index 8bbbc5cc7..1794ad6eb 100644
--- a/source/main.h
+++ b/source/main.h
@@ -21,11 +21,13 @@
 
 #pragma once
 
-#include <cstddef>
+#include <stddef.h>
+
 #include <iostream>
 #include <map>
 #include <string>
 #include <vector>
+
 #ifndef CONSOLE_ONLY
 #include "hdr_fltk.h"
 #include "ui_window.h"
@@ -214,7 +216,7 @@ template <typename... Args> [[noreturn]] void FatalError(std::string_view msg, A
 #endif
     }
 
-    std::exit(9);
+    exit(9);
 }
 
 template <typename... Args> void ProgStatus(std::string_view msg, Args &&...args)
diff --git a/source/poly.cc b/source/poly.cc
index da379a6f6..427d9a714 100644
--- a/source/poly.cc
+++ b/source/poly.cc
@@ -16,7 +16,7 @@
 //
 //------------------------------------------------------------------------
 
-#include <cstddef>
+#include <stddef.h>
 
 #include "poly_local.h"
 #include "sys_macro.h"
@@ -777,7 +777,7 @@ bool polygon_c::ContainsPoint(double x, double y) const
     return true;
 }
 
-static constexpr std::size_t EDGE_BUFFER_SIZE = 32;
+static constexpr size_t EDGE_BUFFER_SIZE = 32;
 
 void polygon_c::ClockwiseOrder()
 {
diff --git a/source/poly.h b/source/poly.h
index b2f5f0999..343befc5f 100644
--- a/source/poly.h
+++ b/source/poly.h
@@ -21,10 +21,11 @@
 // functions provided by the application
 
 #include <stdint.h>
+#include <string.h>
 
-#include <cstring>
 #include <string>
 #include <unordered_map>
+
 void Appl_FatalError(const char *str, ...);
 void Appl_Printf(const char *str, ...);
 
diff --git a/source/poly_map.cc b/source/poly_map.cc
index 01f6a1908..4af0f9f0e 100644
--- a/source/poly_map.cc
+++ b/source/poly_map.cc
@@ -228,11 +228,11 @@ void ParseSectorField(sector_c *sector, const std::string &key, ajparse::token_k
     }
     else if (key == "texturefloor")
     {
-        std::copy(value.data(), value.data() + OBSIDIAN_MIN(8, value.size()), sector->floor_tex);
+        memcpy(sector->floor_tex, value.data(), OBSIDIAN_MIN(8, value.size()));
     }
     else if (key == "textureceiling")
     {
-        std::copy(value.data(), value.data() + OBSIDIAN_MIN(8, value.size()), sector->ceil_tex);
+        memcpy(sector->ceil_tex, value.data(), OBSIDIAN_MIN(8, value.size()));
     }
     else if (key == "lightlevel")
     {
@@ -264,15 +264,15 @@ void ParseSidedefField(sidedef_c *side, const std::string &key, ajparse::token_k
     }
     else if (key == "texturetop")
     {
-        std::copy(value.data(), value.data() + OBSIDIAN_MIN(8, value.size()), side->upper_tex);
+        memcpy(side->upper_tex, value.data(), OBSIDIAN_MIN(8, value.size()));
     }
     else if (key == "texturebottom")
     {
-        std::copy(value.data(), value.data() + OBSIDIAN_MIN(8, value.size()), side->lower_tex);
+        memcpy(side->lower_tex, value.data(), OBSIDIAN_MIN(8, value.size()));
     }
     else if (key == "texturemiddle")
     {
-        std::copy(value.data(), value.data() + OBSIDIAN_MIN(8, value.size()), side->mid_tex);
+        memcpy(side->mid_tex, value.data(), OBSIDIAN_MIN(8, value.size()));
     }
     else if (key == "sector")
     {
@@ -813,8 +813,8 @@ bool LoadSectors()
         sector->floor_h = LE_S16(raw->floorh);
         sector->ceil_h  = LE_S16(raw->ceilh);
 
-        std::copy(raw->floor_tex, raw->floor_tex + 8, sector->floor_tex);
-        std::copy(raw->ceil_tex, raw->ceil_tex + 8, sector->ceil_tex);
+        memcpy(sector->floor_tex, raw->floor_tex, 8);
+        memcpy(sector->ceil_tex, raw->ceil_tex, 8);
 
         sector->light   = LE_U16(raw->light);
         sector->special = LE_U16(raw->type);
@@ -941,9 +941,9 @@ bool LoadSidedefs()
         side->x_offset = LE_S16(raw->x_offset);
         side->y_offset = LE_S16(raw->y_offset);
 
-        std::copy(raw->upper_tex, raw->upper_tex + 8, side->upper_tex);
-        std::copy(raw->mid_tex, raw->mid_tex + 8, side->mid_tex);
-        std::copy(raw->lower_tex, raw->lower_tex + 8, side->lower_tex);
+        memcpy(side->upper_tex, raw->upper_tex, 8);
+        memcpy(side->mid_tex, raw->mid_tex, 8);
+        memcpy(side->lower_tex, raw->lower_tex, 8);
     }
 
     return true; // OK
diff --git a/source/poly_wad.h b/source/poly_wad.h
index fd696b9e7..aeb11243f 100644
--- a/source/poly_wad.h
+++ b/source/poly_wad.h
@@ -18,8 +18,9 @@
 
 #pragma once
 
-#include <cstdio>
-#include <cstring>
+#include <stdio.h>
+#include <string.h>
+
 #include <vector>
 
 // directory entry
diff --git a/source/slump.cc b/source/slump.cc
index 9aa21e778..82cbd156d 100644
--- a/source/slump.cc
+++ b/source/slump.cc
@@ -30,10 +30,9 @@
 #include "slump.h"
 
 #include <assert.h>
+#include <stdlib.h>
 #include <string.h>
 
-#include <cstdlib>
-
 #include "lib_util.h"
 #include "m_lua.h"
 #include "sys_macro.h"
diff --git a/source/slump_dump.cc b/source/slump_dump.cc
index b80896ab3..97f9ddb59 100644
--- a/source/slump_dump.cc
+++ b/source/slump_dump.cc
@@ -30,10 +30,9 @@
  */
 
 #include <assert.h>
+#include <stdlib.h>
 #include <string.h>
 
-#include <cstdlib>
-
 #include "lib_util.h"
 #include "slump.h"
 
diff --git a/source/sys_assert.cc b/source/sys_assert.cc
index 50a01fc9b..850c11ba6 100644
--- a/source/sys_assert.cc
+++ b/source/sys_assert.cc
@@ -19,8 +19,8 @@
 //
 //----------------------------------------------------------------------------
 
-#include "headers.h"
 #include "main.h"
+#include "sys_macro.h"
 
 //----------------------------------------------------------------------------
 
diff --git a/source/sys_debug.cc b/source/sys_debug.cc
index f550ca2ae..1154fa9c9 100644
--- a/source/sys_debug.cc
+++ b/source/sys_debug.cc
@@ -19,11 +19,11 @@
 //
 //------------------------------------------------------------------------
 
-#include <ctime>
+#include <time.h>
+
 #include <fstream>
 #include <iostream>
 
-#include "headers.h"
 #include "lib_util.h"
 #include "m_lua.h"
 #include "main.h"
diff --git a/source/tx_forge.cc b/source/tx_forge.cc
index e1c547d57..8cfe36bc1 100644
--- a/source/tx_forge.cc
+++ b/source/tx_forge.cc
@@ -34,9 +34,10 @@
 
 #include "tx_forge.h"
 
-#include "headers.h"
 #include "lib_util.h"
 #include "main.h"
+#include "sys_assert.h"
+#include "sys_macro.h"
 #include "sys_xoshiro.h"
 
 /* Definitions used to address real and imaginary parts in a two-dimensional
diff --git a/source/tx_skies.cc b/source/tx_skies.cc
index 65412081a..81e01fff9 100644
--- a/source/tx_skies.cc
+++ b/source/tx_skies.cc
@@ -21,10 +21,11 @@
 
 #include "tx_skies.h"
 
-#include "headers.h"
 #include "lib_util.h"
 #include "m_lua.h"
 #include "main.h"
+#include "sys_assert.h"
+#include "sys_macro.h"
 #include "sys_xoshiro.h"
 #include "tx_forge.h"
 
diff --git a/source/ui_build.cc b/source/ui_build.cc
index 0d31ea8b5..9e2dd754c 100644
--- a/source/ui_build.cc
+++ b/source/ui_build.cc
@@ -21,9 +21,10 @@
 
 #include "hdr_fltk.h"
 #include "hdr_ui.h"
-#include "headers.h"
 #include "lib_util.h"
+#include "m_trans.h"
 #include "main.h"
+#include "sys_assert.h"
 
 UI_Build::UI_Build(int X, int Y, int W, int H, const char *label) : Fl_Group(X, Y, W, H, label)
 {
diff --git a/source/ui_game.cc b/source/ui_game.cc
index 66fd5b170..e3be38710 100644
--- a/source/ui_game.cc
+++ b/source/ui_game.cc
@@ -24,9 +24,9 @@
 #include "hdr_fltk.h"
 #include "hdr_lua.h"
 #include "hdr_ui.h"
-#include "headers.h"
 #include "lib_util.h"
 #include "m_lua.h"
+#include "m_trans.h"
 #include "main.h"
 
 #define ABORT_COLOR fl_color_cube(3, 1, 1)
diff --git a/source/ui_game.h b/source/ui_game.h
index f3f4fb645..82c7b88de 100644
--- a/source/ui_game.h
+++ b/source/ui_game.h
@@ -21,7 +21,7 @@
 
 #pragma once
 
-#include <cstddef>
+#include <stddef.h>
 
 #include "FL/Fl_Button.H"
 #include "FL/Fl_Group.H"
diff --git a/source/ui_hyper.cc b/source/ui_hyper.cc
index 7c6722300..87bbb3b72 100644
--- a/source/ui_hyper.cc
+++ b/source/ui_hyper.cc
@@ -27,7 +27,6 @@
 
 #include "hdr_fltk.h"
 #include "hdr_ui.h"
-#include "headers.h"
 #include "lib_util.h"
 #include "main.h"
 
diff --git a/source/ui_map.cc b/source/ui_map.cc
index 48c6757ff..0557f9b6c 100644
--- a/source/ui_map.cc
+++ b/source/ui_map.cc
@@ -24,9 +24,10 @@
 #include "gif.h"
 #include "hdr_fltk.h"
 #include "hdr_ui.h"
-#include "headers.h"
 #include "lib_util.h"
 #include "main.h"
+#include "sys_assert.h"
+#include "sys_macro.h"
 
 // The includes got too messy to make these part of the UI_MiniMap class - Dasho
 static GifWriter *gif_writer;
diff --git a/source/ui_module.cc b/source/ui_module.cc
index 507763815..d16753c7a 100644
--- a/source/ui_module.cc
+++ b/source/ui_module.cc
@@ -24,10 +24,12 @@
 #include "hdr_fltk.h"
 #include "hdr_lua.h"
 #include "hdr_ui.h"
-#include "headers.h"
 #include "lib_util.h"
 #include "m_lua.h"
+#include "m_trans.h"
 #include "main.h"
+#include "sys_assert.h"
+#include "sys_macro.h"
 #include "sys_xoshiro.h"
 
 UI_Module::UI_Module(int X, int Y, int W, int H, std::string id, std::string label, std::string tip, int red, int green,
@@ -337,17 +339,7 @@ void UI_Module::AddSliderOption(std::string opt, std::string label, std::string
     // Populate the preset_choices map
     oldpos = 0;
     pos    = 0;
-#ifdef __APPLE__
     setlocale(LC_NUMERIC, "C");
-#elif __unix__
-#ifndef __linux__
-    setlocale(LC_NUMERIC, "C");
-#else
-    std::setlocale(LC_NUMERIC, "C");
-#endif
-#else
-    std::setlocale(LC_NUMERIC, "C");
-#endif
 
     while (pos != std::string::npos)
     {
@@ -363,7 +355,7 @@ void UI_Module::AddSliderOption(std::string opt, std::string label, std::string
             double key;
             try
             {
-                key                      = std::stod(map_string.substr(0, temp_pos));
+                key                      = stod(map_string.substr(0, temp_pos));
                 std::string value        = map_string.substr(temp_pos + 1);
                 rsl->preset_choices[key] = value;
             }
@@ -388,17 +380,8 @@ void UI_Module::AddSliderOption(std::string opt, std::string label, std::string
             oldpos = pos + 1;
         }
     }
-#ifdef __APPLE__
+    
     setlocale(LC_NUMERIC, numeric_locale.c_str());
-#elif __unix__
-#ifndef __linux__
-    setlocale(LC_NUMERIC, numeric_locale.c_str());
-#else
-    std::setlocale(LC_NUMERIC, numeric_locale.c_str());
-#endif
-#else
-    std::setlocale(LC_NUMERIC, numeric_locale.c_str());
-#endif
 
     rsl->cb_data           = new opt_change_callback_data_t;
     rsl->cb_data->mod      = rsl;
@@ -682,7 +665,7 @@ bool UI_Module::SetSliderOption(std::string option, std::string value)
     double double_value;
     try
     {
-        double_value = std::stod(value);
+        double_value = stod(value);
         if (limit_break)
         {
             rsl->mod_slider->value(double_value);
@@ -1023,7 +1006,7 @@ void UI_Module::callback_ManualEntry(Fl_Widget *w, void *data)
 
     try
     {
-        new_value = std::stod(string_value);
+        new_value = stod(string_value);
     }
     catch (std::invalid_argument &e)
     {
diff --git a/source/ui_widgets.cc b/source/ui_widgets.cc
index 908014741..74255b58c 100644
--- a/source/ui_widgets.cc
+++ b/source/ui_widgets.cc
@@ -21,10 +21,11 @@
 
 #include "hdr_fltk.h"
 #include "hdr_ui.h"
-#include "headers.h"
 #include "lib_util.h"
 #include "m_lua.h"
+#include "m_trans.h"
 #include "main.h"
+#include "sys_assert.h"
 
 choice_data_c::choice_data_c(std::string _id, std::string _label) : enabled(false), mapped(-1), widget(NULL)
 {
diff --git a/source/ui_window.cc b/source/ui_window.cc
index 0a9461727..d82ec2107 100644
--- a/source/ui_window.cc
+++ b/source/ui_window.cc
@@ -19,14 +19,14 @@
 //
 //------------------------------------------------------------------------
 
+#ifndef _WIN32
+#include <unistd.h>
+#endif
+
 #include "hdr_fltk.h"
 #include "hdr_ui.h"
-#include "headers.h"
 #include "main.h"
-
-#ifndef WIN32
-#include <unistd.h>
-#endif
+#include "m_trans.h"
 
 #if (FL_MAJOR_VERSION != 1 || FL_MINOR_VERSION < 3)
 #error "Require FLTK version 1.3.0 or later"