Qt: Add translation support (#664)

* Translation PoC

* i18n but better

* More Greek translation

* Add proper translation UI

* Linux CI: Install qt6-tools-dev

include/frontend_settings.hpp

@@ -24,6 +24,7 @@ struct FrontendSettings {
 
 	Theme theme = Theme::Dark;
 	WindowIcon icon = WindowIcon::Rpog;
+	std::string language = "en";
 
 	static Theme themeFromString(std::string inString);
 	static const char* themeToString(Theme theme);

include/panda_qt/config_window.hpp

@@ -45,6 +45,8 @@ class ConfigWindow : public QDialog {
 	void setTheme(FrontendSettings::Theme theme);
 	void setIcon(FrontendSettings::WindowIcon icon);
 
+	QComboBox* createLanguageSelect();
+
   public:
 	ConfigWindow(ConfigCallback configCallback, MainWindowCallback windowCallback, const EmulatorConfig& config, QWidget* parent = nullptr);
 	~ConfigWindow();

include/panda_qt/main_window.hpp

@@ -126,6 +126,7 @@ class MainWindow : public QMainWindow {
 	void setupControllerSensors(SDL_GameController* controller);
 	void sendMessage(const EmulatorMessage& message);
 	void dispatchMessage(const EmulatorMessage& message);
+	void loadTranslation();
 
 	// Tracks whether we are using an OpenGL-backed renderer or a Vulkan-backed renderer
 	bool usingGL = false;