macOS: fix locale detection

builtin/mainmenu/tab_local.lua

@@ -16,6 +16,8 @@
 --51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
 local lang = core.settings:get("language")
+if not (lang and (lang ~= "")) then lang = os.getenv("LANG") end
+
 local function get_formspec()
 	local index = filterlist.get_current_index(menudata.worldlist,
 				tonumber(core.settings:get("mainmenu_last_selected_world")))

src/gettext.cpp

@@ -226,6 +226,7 @@ void init_gettext(const char *path, const std::string &configured_language,
 		NSString *syslang = [[NSLocale preferredLanguages] firstObject];
 		[syslang getBytes:lang maxLength:2 usedLength:nil encoding:NSASCIIStringEncoding options:0 range:NSMakeRange(0, 2) remainingRange:nil];
 		setenv("LANGUAGE", lang, 1);
+		setenv("LANG", lang, 1);
 #endif
 		setlocale(LC_ALL, "");
 	}