Reset \XeTeXlinebreaklocale when nested language is closed

Since this is a global setting, it must be explicitly reset.
To this end, we introduce the new hook \nestedextras@<language>
which is executed after a nested language has been closed.

doc/polyglossia.tex

@@ -2330,14 +2330,15 @@ \section{Modifying or extending captions, date formats and language settings}
 	          \meta{lang} is activated locally via \cmd\text\meta{lang} command
 	\item \Cmd{\noextras@\meta{lang}} stores macros that are to be executed when the language
 	          \meta{lang} is closed
+	\item \Cmd{\nestedextras@\meta{lang}}\new{2.3} stores macros that are to be executed when a nested language
+	          is closed and \meta{lang} is the active language again. This is useful
+	          for settings that are only possible on global scale.
 \end{itemize}
 %
-In order to redefine internal macros, we recommend to use the command \cmd\gappto.
-For compatibility with \pkg{babel} the command \cmd\addto\ is also available
-to the same effect. For instance, to change the \cmd\chaptername\ for language ¦lingua¦,
-you can do this:
+In order to redefine internal macros, we recommend to use the command \cmd\addto.
+For instance, to change the \cmd\chaptername\ for language ¦lingua¦, you can do this:
 \begin{verbatim}
-\gappto\captionslingua{\def\chaptername{Caput}}
+\addto\captionslingua{\def\chaptername{Caput}}
 \end{verbatim}
 %
 Note that this needs to be done after the respective language has been loaded with

tex/gloss-chinese.ldf

@@ -310,12 +310,14 @@
   \@ifundefined{xpg@orig@XeTeXlinebreakskip}{\newskip\xpg@orig@XeTeXlinebreakskip}{}
   \xpg@orig@XeTeXlinebreakskip=\XeTeXlinebreakskip
   \def\chinese@simplified@spacing{%
-    \XeTeXlinebreaklocale "zh"
-    \XeTeXlinebreakskip = 0pt plus 0.1em minus 0.01em}
+    \XeTeXlinebreaklocale "zh"%
+    \XeTeXlinebreakskip = 0pt plus 0.1em minus 0.01em%
+  }
   \let\chinese@traditional@spacing\chinese@simplified@spacing
   \def\nochinese@spacing{%
-    \XeTeXlinebreakskip=\xpg@orig@XeTeXlinebreakskip
-    \XeTeXlinebreaklocale ""}
+    \XeTeXlinebreakskip=\xpg@orig@XeTeXlinebreakskip%
+    \XeTeXlinebreaklocale ""%
+  }
 \fi
 
 \def\noextras@chinese{%
@@ -340,5 +342,18 @@
       \chinese@simplified@spacing%
     \fi%
 }
+
+\ifxetex
+  % \XeTeXlinebreaklocale is global,
+  % so we need to reset after nested language got closed
+  \def\nestedextras@chinese{%
+    \ifchinese@traditional
+      \chinese@traditional@spacing%
+    \else
+      \chinese@simplified@spacing%
+    \fi%
+  }
+\fi
+
 % Based on contributions of Toru Inagaki, Norio Iwase, François Charette
 

tex/gloss-japanese.ldf

@@ -248,11 +248,13 @@
   \@ifundefined{xpg@orig@XeTeXlinebreakskip}{\newskip\xpg@orig@XeTeXlinebreakskip}{}
   \xpg@orig@XeTeXlinebreakskip=\XeTeXlinebreakskip
   \def\japanese@spacing{%
-    \XeTeXlinebreaklocale "ja"
-    \XeTeXlinebreakskip = 0pt plus 0.1em minus 0.01em}
+    \XeTeXlinebreaklocale "ja"%
+    \XeTeXlinebreakskip = 0pt plus 0.1em minus 0.01em%
+  }
   \def\nojapanese@spacing{%
-    \XeTeXlinebreakskip=\xpg@orig@XeTeXlinebreakskip
-    \XeTeXlinebreaklocale ""}
+    \XeTeXlinebreakskip=\xpg@orig@XeTeXlinebreakskip%
+    \XeTeXlinebreaklocale ""%
+   }
 \fi
 
 \def\noextras@japanese{%
@@ -269,5 +271,14 @@
   \japanese@capsformat%
   \japanese@spacing%
 }
+
+\ifxetex
+  % \XeTeXlinebreaklocale is global,
+  % so we need to reset after nested language got closed
+  \def\nestedextras@japanese{%
+    \japanese@spacing%
+  }
+\fi
+
 % Based on contributions of Toru Inagaki, Norio Iwase, François Charette
 

tex/gloss-korean.ldf

@@ -432,6 +432,11 @@
         \XeTeXlinebreaklocale ""
         \noextras@korean@common
     }
+    % \XeTeXlinebreaklocale is global,
+    % so we need to reset after nested language got closed
+    \def\nestedextras@korean{%
+      \XeTeXlinebreaklocale "ko"%
+    }
 \else % luatex
     \def\inlineextras@korean{\xpg@attr@cjkspacing\xpg@korean@variant\relax}
     \def\noextras@korean{%

tex/polyglossia.sty

@@ -1708,6 +1708,7 @@
       \xpg_otherlanguage:nn{ \xpg_alias_add_to_option_i:nn{#2}{#1} }{ #3 }
       \__xpg_lang_set_text_direction:nn{#3}{#4}
     \group_end:
+    \cs_if_exist_use:c{ nestedextras@\languagename }
   }
 }
 \cs_generate_variant:Nn \__xpg_foreignlanguage:nnnn {eeen}
@@ -1719,6 +1720,7 @@
 	\__xpg_otherlanguage:eee { #1 } { #2 } { \xpg_alias_base_lang:n { #2 } }
   }{
 	\c_group_end_token% \group_end: does not work here!
+	\cs_if_exist_use:c{ nestedextras@\languagename }
   }
 
 % internal wrapper
@@ -1770,6 +1772,7 @@
       \cs_if_exist_use:c{date@bbl@\babelname}
       \__xpg_lang_set_text_direction:nn{#3}{#4}
     \group_end:
+    \cs_if_exist_use:c{ nestedextras@\languagename }
   }
 }
 \cs_generate_variant:Nn \__xpg_textlanguage:nnnn {nnen}