I tried this, and it crashed after saying it would reboot to load the language pack. It did not crash when I logged in, but also the language was not changed for me either. Main client, Win 7.

LoopHashLibrary: Reading merged bbdb_ (BackboneDatabase) with extras
LoopHashLibrary: Reading cmp-database-b045b55dc83ee303ba2fcb4992a2c251\database\loop_hash\backbone.db.gz
BackboneDB: Reading in proteins 0 to 3598 out of 3598 , partition: 1/1
ViewOptionsWidget::refresh()
SAVING LOCALE OPTIONS

UNHANDLED EXCEPTION
1: RaiseException +88 bytes (no line)
2: library_main +33237349 bytes (no line)
3: library_main +322219 bytes (no line)
4: library_main +3456240 bytes (no line)
5: library_main +1149744 bytes (no line)
6: library_main +1460003 bytes (no line)
7: library_main +4381492 bytes (no line)
8: library_main +4147700 bytes (no line)
9: library_main +4151046 bytes (no line)
10: library_main +4298462 bytes (no line)
11: library_main +3987796 bytes (no line)
12: library_main +5890569 bytes (no line)
13: library_main +3987001 bytes (no line)
14: library_main +5897124 bytes (no line)
15: library_main +5899437 bytes (no line)
16: gapfnScSendMessage +818 bytes (no line)
17: GetThreadDesktop +215 bytes (no line)
18: GetClientRect +197 bytes (no line)
19: CallWindowProcW +27 bytes (no line)
20: wglSwapBuffers +730 bytes (no line)
21: gapfnScSendMessage +818 bytes (no line)
22: GetThreadDesktop +215 bytes (no line)
23: CharPrevW +312 bytes (no line)
24: DispatchMessageA +15 bytes (no line)
25: library_main +5904835 bytes (no line)
26: library_main +3855995 bytes (no line)
27: library_main +32708 bytes (no line)
28: library_main +29 bytes (no line)
29: no symbol (no line)
30: no symbol (no line)
31: no symbol (no line)
32: BaseThreadInitThunk +18 bytes (no line)
33: RtlInitializeExceptionChain +99 bytes (no line)
34: RtlInitializeExceptionChain +54 bytes (no line)

Reproduced this issue and forwarded it to developers during a meeting yesterday. Thank you for the feedback Startrek and thank you Brow for including a crash log.

It's the same for me with french on Win 7 64.

Update: This issue is now fixed in the current devprev build.

This seems to be fixed in the current release. Cleaning up the feedback list.