frontend: Use system locale instead of 'C'

Sets runtime locale to system locale with UTF-8 codepage. This is already default behavior on unix, but Windows defaults to minimal 'C' locale.

Use CRT locale for C++ std::locale default

OBS Studio language settings no longer change QLocale default locale, instead system locale is used for conformity. It is likely this is what user wants as well. Ie. sorting and formatting functions should follow OS locale instead of OBS Studio language (which also lacks country information).

Author: Dankirk

frontend/OBSApp.cpp

@@ -724,11 +724,6 @@ bool OBSApp::InitLocale()
 
 	locale = lang;
 
-	// set basic default application locale
-	if (!locale.empty()) {
-		QLocale::setDefault(QLocale(QString::fromStdString(locale).replace('-', '_')));
-	}
-
 	string englishPath;
 	if (!GetDataFilePath("locale/" DEFAULT_LANG ".ini", englishPath)) {
 		OBSErrorBox(NULL, "Failed to find locale/" DEFAULT_LANG ".ini");
@@ -768,11 +763,6 @@ bool OBSApp::InitLocale()
 			blog(LOG_INFO, "Using preferred locale '%s'", locale_.c_str());
 			locale = locale_;
 
-			// set application default locale to the new chosen one
-			if (!locale.empty()) {
-				QLocale::setDefault(QLocale(QString::fromStdString(locale).replace('-', '_')));
-			}
-
 			return true;
 		}
 
@@ -914,13 +904,6 @@ OBSApp::OBSApp(int &argc, char **argv, profiler_name_store_t *store)
 {
 	installNativeEventFilter(new OBS::NativeEventFilter);
 
-	/* fix float handling */
-#if defined(Q_OS_UNIX)
-	if (!setlocale(LC_NUMERIC, "C")) {
-		blog(LOG_WARNING, "Failed to set LC_NUMERIC to C locale");
-	}
-#endif
-
 #ifndef _WIN32
 	// Add POSIX signal handlers:
 	// * SIGINT

frontend/obs-main.cpp

@@ -45,6 +45,7 @@
 #include <shellapi.h>
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
+#include <mbctype.h>
 #else
 #include <signal.h>
 #endif
@@ -77,6 +78,7 @@ bool opt_disable_missing_files_check = false;
 string opt_starting_collection;
 string opt_starting_profile;
 string opt_starting_scene;
+bool using_utf8 = false;
 
 bool restart = false;
 bool restart_safe = false;
@@ -416,6 +418,42 @@ static void create_log_file(fstream &logFile)
 	}
 }
 
+static bool set_utf8_locale(void)
+{
+	// Use system locale with UTF-8 codepage (available from Windows 10 version 1803)
+	bool usingUTF8 = !!setlocale(LC_ALL, ".UTF-8");
+
+	/*
+	Fallback to minimal C locale
+	Could use "" for system defaults, but the Windows default ANSI codepages (such as .125x or .9xx)
+	mismatch with UTF-8 that is assumed by many parts of the codebase. "C" only covers ASCII, so no mismatches.
+	*/
+	usingUTF8 = usingUTF8 || !!setlocale(LC_ALL, "C.UTF-8");
+
+#ifdef _WIN32
+	usingUTF8 = usingUTF8 && (_setmbcp(CP_UTF8) == 0);
+#endif
+	if (!usingUTF8) {
+		setlocale(LC_ALL, "C");
+	}
+
+	// fix float handling
+	setlocale(LC_NUMERIC, "C");
+
+	// Copy C runtime locale for C++
+	std::locale defaultLocale(setlocale(LC_ALL, nullptr));
+	std::locale::global(defaultLocale);
+
+	/*
+	system() is already the QLocale default, but just to be explicit about the intention.
+	Unlike CRT and C++ locales above, QLocale doesn't support customization of locale categories and codepages.
+	Ie. We can't enforce decimal point to be a dot and at the same time use user's preferred locale.
+	*/
+	QLocale::setDefault(QLocale::system());
+
+	return usingUTF8;
+}
+
 static auto ProfilerNameStoreRelease = [](profiler_name_store_t *store) {
 	profiler_name_store_free(store);
 };
@@ -533,6 +571,12 @@ static int run_program(fstream &logFile, int argc, char *argv[])
 	qputenv("QT_NO_SUBTRACTOPAQUESIBLINGS", "1");
 
 	OBSApp program(argc, argv, profilerNameStore.get());
+
+#if defined(Q_OS_UNIX)
+	// OBSApp (QApplication) constructor overwrote the locale for unix, so set it again
+	set_utf8_locale();
+#endif
+
 	try {
 		QAccessible::installFactory(accessibleFactory);
 		QFontDatabase::addApplicationFont(":/fonts/OpenSans-Regular.ttf");
@@ -683,6 +727,15 @@ static int run_program(fstream &logFile, int argc, char *argv[])
 			blog(LOG_INFO, "Command Line Arguments: %s", stor.str().c_str());
 		}
 
+		if (!using_utf8) {
+			blog(LOG_DEBUG, "UTF-8 locale is not available on this OS version. "
+					"Skipping regional formatting and sorting.");
+		}
+
+		// Use collation (sorting rules) as indicator of regional settings
+		blog(LOG_DEBUG, "Locale: %s", setlocale(LC_COLLATE, nullptr));
+		blog(LOG_DEBUG, "App language: %s", program.GetLocale());
+
 		if (!program.OBSInit()) {
 			return 0;
 		}
@@ -903,6 +956,7 @@ static void set_process_mitigation_policies()
 
 int main(int argc, char *argv[])
 {
+	using_utf8 = set_utf8_locale();
 #ifndef _WIN32
 	using SignalHandlerCallback = decltype(OBSApp::sigIntSignalHandler);