AGS: Internal/default language selection issue

[scureuil]

(tested with build windows-x86-64-master-bde92c14, 1-Jun-2021, on Windows 10)

Issue for language selection:

if an AGS game has its language changed with winsetup.exe,

setting game language to "default" in ScummVM uses this language setting, and not the "Game Default" one.

This makes selection of the internal language impossible in ScummVM.

i.e. Maniac Mansion Mania 2 "Game Default" language is german, but after changing "Game language" in winsetup.exe to "English translation", both "default" and "english" in ScummVM (the only available choices) select "english".