Add utility functions for GameCube language codes

Source/Core/Core/BootManager.cpp

@@ -393,9 +393,8 @@ bool BootCore(std::unique_ptr<BootParameters> boot, const WindowSystemInfo& wsi)
   // Override out-of-region languages/countries to prevent games from crashing or behaving oddly
   if (!StartUp.bOverrideRegionSettings)
   {
-    const int gc_language =
-        static_cast<int>(StartUp.GetLanguageAdjustedForRegion(false, StartUp.m_region));
-    StartUp.SelectedLanguage = gc_language - (gc_language > 0);
+    StartUp.SelectedLanguage =
+        DiscIO::ToGameCubeLanguage(StartUp.GetLanguageAdjustedForRegion(false, StartUp.m_region));
 
     if (StartUp.bWii)
     {

Source/Core/Core/ConfigManager.cpp

@@ -963,12 +963,11 @@ DiscIO::Region SConfig::GetFallbackRegion()
 
 DiscIO::Language SConfig::GetCurrentLanguage(bool wii) const
 {
-  int language_value;
+  DiscIO::Language language;
   if (wii)
-    language_value = Config::Get(Config::SYSCONF_LANGUAGE);
+    language = static_cast<DiscIO::Language>(Config::Get(Config::SYSCONF_LANGUAGE));
   else
-    language_value = SConfig::GetInstance().SelectedLanguage + 1;
-  DiscIO::Language language = static_cast<DiscIO::Language>(language_value);
+    language = DiscIO::FromGameCubeLanguage(SConfig::GetInstance().SelectedLanguage);
 
   // Get rid of invalid values (probably doesn't matter, but might as well do it)
   if (language > DiscIO::Language::Unknown || language < DiscIO::Language::Japanese)

Source/Core/DiscIO/Enums.cpp

@@ -126,6 +126,22 @@ bool IsNTSC(Region region)
   return region == Region::NTSC_J || region == Region::NTSC_U || region == Region::NTSC_K;
 }
 
+int ToGameCubeLanguage(Language language)
+{
+  if (language < Language::English || language > Language::Dutch)
+    return 0;
+  else
+    return static_cast<int>(language) - 1;
+}
+
+Language FromGameCubeLanguage(int language)
+{
+  if (language < 0 || language > 5)
+    return Language::Unknown;
+  else
+    return static_cast<Language>(language + 1);
+}
+
 // Increment CACHE_REVISION (GameFileCache.cpp) if the code below is modified
 
 Country TypicalCountryForRegion(Region region)

Source/Core/DiscIO/Enums.h

@@ -76,6 +76,9 @@ bool IsDisc(Platform volume_type);
 bool IsWii(Platform volume_type);
 bool IsNTSC(Region region);
 
+int ToGameCubeLanguage(Language language);
+Language FromGameCubeLanguage(int language);
+
 Country TypicalCountryForRegion(Region region);
 Region SysConfCountryToRegion(u8 country_code);
 // Avoid using this function if you can. Country codes aren't always reliable region indicators.