User interface language isn't properly shown in Options dialog

After opening Tools -> Options, the "user interface language" setting always shows default "<System Language>" option.

Steps to reproduce the most annoying case, i.e. when you change another options and accidentally reset the language:

1. Start QtCreator
2. Select Tools -> Options
3. Select anything else than <System Language>
4. Click OK
5. You'll be informed that you have to restart QtCreator after language change
6. Restart QtCreator
7. User interface should use the language you selected before
8. Select Tools -> Options
9. Notice that "user interface language" shows "<System Language>" instead of language selected before
10. Change some other options
11. Click OK
12. You'll be informed that you have to restart QtCreator after language change
13. Restart QtCreator
14. User interface will use system language