Fix #18433: TTF fonts can not be located when font names are translated

The issue here is that fontconfig may report the name of a given
font face in a language specified by the current locale, while the
OpenRCT2 font code checks the result against an English name.

This fix addresses the issue by temporarily changing the environment
LANG variable to use the default C locale, which should guarantee
English/ASCII names are returned by fontconfig. It uses an RAII
mechanism to ensure that the modified environment variable is restored
to its original value on exiting GetFontPath.

distribution/changelog.txt

@@ -12,6 +12,7 @@
 - Fix: [#18376] Ghost train gentle to flat track is not visible in tunnels.
 - Fix: [#18389] Gentle sloped track pieces are not visible in low clearance height tunnels (original bug).
 - Fix: [#18423] Underground Mini Golf holes can draw over land edges (original bug).
+- Fix: [#18433] CJK TrueType fonts could not be located when font names are translated by the OS.
 - Fix: [#18436] Scenery on the same tile as steep to vertical track can draw over the track (original bug).
 - Fix: [#18711] Park entrances with their sides underground can cause glitching.
 - Fix: [#20848] Junior Roller Coaster booster track does not draw correctly in tunnels.

src/openrct2/platform/Platform.Linux.cpp

@@ -16,6 +16,7 @@
     #include <limits.h>
     #include <locale.h>
     #include <pwd.h>
+    #include <stdlib.h>
     #include <unistd.h>
     #include <vector>
     #if defined(__FreeBSD__) || defined(__NetBSD__)
@@ -39,6 +40,43 @@
 
 namespace OpenRCT2::Platform
 {
+    // EnvLangGuard allows us to temporarily set the user's locale
+    // to the generic C locale, in order to trick fontconfig into
+    // returning an English font face name, while using RAII to avoid
+    // changing locale settings in other parts of the program
+    class EnvLangGuard
+    {
+    public:
+        EnvLangGuard();
+        ~EnvLangGuard();
+
+    private:
+        // GNU recommends scripts/programs set LC_ALL to override
+        // locales for uniform testing, clearing it after should let
+        // LANG and other locale settings operate normally
+        static constexpr const char* _kOverrideVarName{ "LC_ALL" };
+        static constexpr const char* _kTargetLocale{ "C.UTF-8" };
+    };
+
+    EnvLangGuard::EnvLangGuard()
+    {
+        int overwrite = 1;
+        int result = setenv(_kOverrideVarName, _kTargetLocale, overwrite);
+        if (result != 0)
+        {
+            LOG_VERBOSE("Could not update locale for font selection, some fonts may display incorrectly");
+        }
+    }
+
+    EnvLangGuard::~EnvLangGuard()
+    {
+        int result = unsetenv(_kOverrideVarName);
+        if (result != 0)
+        {
+            LOG_VERBOSE("Could not restore user locale");
+        }
+    }
+
     std::string GetFolderPath(SPECIAL_FOLDER folder)
     {
         switch (folder)
@@ -352,6 +390,10 @@ namespace OpenRCT2::Platform
     #ifndef NO_TTF
     std::string GetFontPath(const TTFFontDescriptor& font)
     {
+        // set LANG to portable C.UTF-8 so font face names from fontconfig
+        // are reported in English
+        EnvLangGuard elg;
+
         LOG_VERBOSE("Looking for font %s with FontConfig.", font.font_name);
         FcConfig* config = FcInitLoadConfigAndFonts();
         if (!config)