locale: Implemented SDL_GetPreferredLocales().

This was something I proposed a long time ago, Sylvain Becker did
additional work on it, then back to me.

Fixes Bugzilla #2131.

src/main/haiku/SDL_BApp.h

@@ -22,6 +22,7 @@
 #define SDL_BAPP_H
 
 #include <InterfaceKit.h>
+#include <LocaleRoster.h>
 #if SDL_VIDEO_OPENGL
 #include <OpenGLKit.h>
 #endif
@@ -153,6 +154,10 @@ public:
             _HandleWindowResized(message);
             break;
 
+        case B_LOCALE_CHANGED:
+            SDL_SendLocaleChangedEvent();
+            break;
+
         case BAPP_SCREEN_CHANGED:
             /* TODO: Handle screen resize or workspace change */
             break;