Add a `--lang` command line argument

This allows forcing the locale without changing the settings.

The `forceLocale` option also lets us avoid changing the locale in settings if fonts.mpq is missing, fixing the following scenario:
1. System locale is ja
2. Launch the game -- fonts are missing
3. Close the game, download fonts.mpq
4. Launch the game again -- it is now in English because the settings have changed

Source/diablo.cpp

@@ -907,6 +907,7 @@ void PrintHelpOption(string_view flags, string_view description)
 	PrintHelpOption("--data-dir", _(/* TRANSLATORS: Commandline Option */ "Specify the folder of diabdat.mpq"));
 	PrintHelpOption("--save-dir", _(/* TRANSLATORS: Commandline Option */ "Specify the folder of save files"));
 	PrintHelpOption("--config-dir", _(/* TRANSLATORS: Commandline Option */ "Specify the location of diablo.ini"));
+	PrintHelpOption("--lang", _(/* TRANSLATORS: Commandline Option */ "Specify the language code (e.g. en or pt_BR)"));
 	PrintHelpOption("-n", _(/* TRANSLATORS: Commandline Option */ "Skip startup videos"));
 	PrintHelpOption("-f", _(/* TRANSLATORS: Commandline Option */ "Display frames per second"));
 	PrintHelpOption("--verbose", _(/* TRANSLATORS: Commandline Option */ "Enable verbose logging"));
@@ -939,7 +940,7 @@ void PrintHelpOption(string_view flags, string_view description)
 void PrintFlagsRequiresArgument(string_view flag)
 {
 	printInConsole(flag);
-	printInConsole("requires an argument");
+	printInConsole(" requires an argument");
 	printNewlineInConsole();
 }
 
@@ -968,26 +969,32 @@ void DiabloParseFlags(int argc, char **argv)
 		} else if (arg == "--data-dir") {
 			if (i + 1 == argc) {
 				PrintFlagsRequiresArgument("--data-dir");
-				diablo_quit(0);
+				diablo_quit(64);
 			}
 			paths::SetBasePath(argv[++i]);
 		} else if (arg == "--save-dir") {
 			if (i + 1 == argc) {
 				PrintFlagsRequiresArgument("--save-dir");
-				diablo_quit(0);
+				diablo_quit(64);
 			}
 			paths::SetPrefPath(argv[++i]);
 		} else if (arg == "--config-dir") {
 			if (i + 1 == argc) {
 				PrintFlagsRequiresArgument("--config-dir");
-				diablo_quit(0);
+				diablo_quit(64);
 			}
 			paths::SetConfigPath(argv[++i]);
+		} else if (arg == "--lang") {
+			if (i + 1 == argc) {
+				PrintFlagsRequiresArgument("--lang");
+				diablo_quit(64);
+			}
+			forceLocale = argv[++i];
 #ifndef DISABLE_DEMOMODE
 		} else if (arg == "--demo") {
 			if (i + 1 == argc) {
 				PrintFlagsRequiresArgument("--demo");
-				diablo_quit(0);
+				diablo_quit(64);
 			}
 			demoNumber = SDL_atoi(argv[++i]);
 			gbShowIntro = false;
@@ -996,7 +1003,7 @@ void DiabloParseFlags(int argc, char **argv)
 		} else if (arg == "--record") {
 			if (i + 1 == argc) {
 				PrintFlagsRequiresArgument("--record");
-				diablo_quit(0);
+				diablo_quit(64);
 			}
 			recordNumber = SDL_atoi(argv[++i]);
 		} else if (arg == "--create-reference") {

Source/init.cpp

@@ -216,7 +216,7 @@ void LoadLanguageArchive()
 	lang_mpq = std::nullopt;
 #endif
 
-	string_view code = *sgOptions.Language.code;
+	string_view code = GetLanguageCode();
 	if (code != "en") {
 		std::string langMpqName { code };
 #ifdef UNPACKED_MPQS

Source/utils/language.cpp

@@ -19,6 +19,8 @@
 
 #define MO_MAGIC 0x950412de
 
+std::string forceLocale;
+
 namespace {
 
 using namespace devilution;
@@ -112,16 +114,16 @@ string_view TrimRight(string_view str)
 	return str;
 }
 
-// English, Danish, Spanish, Italian, Swedish
-unsigned PluralForms = 2;
-tl::function_ref<int(int n)> GetLocalPluralId = [](int n) -> int { return n != 1 ? 1 : 0; };
-
 /** plural=(n != 1); */
 int PluralIfNotOne(int n)
 {
 	return n != 1 ? 1 : 0;
 }
 
+// English, Danish, Spanish, Italian, Swedish
+unsigned PluralForms = 2;
+tl::function_ref<int(int n)> GetLocalPluralId = PluralIfNotOne;
+
 /**
  * Match plural=(n != 1);"
  */
@@ -148,7 +150,7 @@ void SetPluralForm(string_view expression)
 
 	// en, bg, da, de, es, it, sv
 	if (expression == "(n != 1)") {
-		GetLocalPluralId = &PluralIfNotOne;
+		GetLocalPluralId = PluralIfNotOne;
 		return;
 	}
 
@@ -340,9 +342,16 @@ bool HasTranslation(const std::string &locale)
 	});
 }
 
+string_view GetLanguageCode()
+{
+	if (!forceLocale.empty())
+		return forceLocale;
+	return *sgOptions.Language.code;
+}
+
 bool IsSmallFontTall()
 {
-	const string_view code = (*sgOptions.Language.code).substr(0, 2);
+	const string_view code = GetLanguageCode().substr(0, 2);
 	return code == "zh" || code == "ja" || code == "ko";
 }
 
@@ -356,14 +365,14 @@ void LanguageInitialize()
 		UiErrorOkDialog(
 		    "Missing fonts.mpq",
 		    StrCat("fonts.mpq is required for locale \"",
-		        *sgOptions.Language.code,
+		        GetLanguageCode(),
 		        "\"\n\n"
 		        "Please download fonts.mpq from:\n"
 		        "github.com/diasurgical/\ndevilutionx-assets/releases"));
-		sgOptions.Language.code = "en";
+		forceLocale = "en";
 	}
 
-	const std::string lang(*sgOptions.Language.code);
+	const std::string lang(GetLanguageCode());
 
 	AssetHandle handle;
 	const uint32_t loadTranslationsStart = SDL_GetTicks();
@@ -377,7 +386,9 @@ void LanguageInitialize()
 			break;
 	}
 	if (!handle.ok()) {
-		GetLocalPluralId = &PluralIfNotOne; // Reset to English plural form
+		// Reset to English, which is always available:
+		forceLocale = "en";
+		GetLocalPluralId = PluralIfNotOne;
 		return;
 	}
 

Source/utils/language.h

@@ -10,6 +10,10 @@
 #define N_(x) (x)
 #define P_(context, x) (x)
 
+extern std::string forceLocale;
+
+devilution::string_view GetLanguageCode();
+
 bool HasTranslation(const std::string &locale);
 void LanguageInitialize();
 

tools/measure_timedemo_performance.py

@@ -15,7 +15,7 @@ class RunMetrics(NamedTuple):
 
 def measure(binary: str) -> RunMetrics:
 	result: subprocess.CompletedProcess = subprocess.run(
-		[binary, '--diablo', '--spawn', '--demo', '0', '--timedemo'], capture_output=True)
+		[binary, '--diablo', '--spawn', '--lang', 'en', '--demo', '0', '--timedemo'], capture_output=True)
 	match = _TIME_AND_FPS_REGEX.search(result.stderr)
 	if not match:
 		raise Exception(f"Failed to parse output in:\n{result.stderr}")