X11 shell locale detection (#1756)

CHANGELOG.md

@@ -71,6 +71,7 @@ You can find its changes [documented below](#070---2021-01-01).
 - Fixed `WindowLevel::Tooltip` on Windows platform ([#1737] by [@djeedai])
 - X11 backend now supports scaling([#1751] by [@Maan2003])
 - X11 backend now supports changing cursors ([#1755] by [@Maan2003])
+- X11 backend now uses the platform locale ([#1756] by [@Maan2003])
 
 ### Visual
 
@@ -710,6 +711,7 @@ Last release without a changelog :(
 [#1751]: https://github.com/linebender/druid/pull/1751
 [#1754]: https://github.com/linebender/druid/pull/1754
 [#1755]: https://github.com/linebender/druid/pull/1755
+[#1756]: https://github.com/linebender/druid/pull/1756
 
 [Unreleased]: https://github.com/linebender/druid/compare/v0.7.0...master
 [0.7.0]: https://github.com/linebender/druid/compare/v0.6.0...v0.7.0

druid-shell/src/platform/x11/application.rs

@@ -526,9 +526,22 @@ impl Application {
     }
 
     pub fn get_locale() -> String {
-        // TODO(x11/locales): implement Application::get_locale
-        tracing::warn!("Application::get_locale is currently unimplemented for X11 platforms. (defaulting to en-US)");
-        "en-US".into()
+        let var_non_empty = |var| match std::env::var(var) {
+            Ok(s) if s.is_empty() => None,
+            Ok(s) => Some(s),
+            Err(_) => None,
+        };
+
+        // from gettext manual
+        // https://www.gnu.org/software/gettext/manual/html_node/Locale-Environment-Variables.html#Locale-Environment-Variables
+        var_non_empty("LANGUAGE")
+            // the LANGUAGE value is priority list seperated by :
+            // See: https://www.gnu.org/software/gettext/manual/html_node/The-LANGUAGE-variable.html#The-LANGUAGE-variable
+            .and_then(|locale| locale.split(':').next().map(String::from))
+            .or_else(|| var_non_empty("LC_ALL"))
+            .or_else(|| var_non_empty("LC_MESSAGES"))
+            .or_else(|| var_non_empty("LANG"))
+            .unwrap_or_else(|| "en-US".to_string())
     }
 
     pub(crate) fn idle_pipe(&self) -> RawFd {