I've found a way to replicate it (at least in my environment)
1. Housekeeping - resetting profile doesn't fix the saving issue so i ve uninstalled all translation via simple-press language page.
2. Resetting profiles now works and you can save your data.
3. Install the translations again
4. Reset profiles in housekeeping page
5. I ve the issue again
I think there is something that translates the slugs at housekeeping process. I'll probably check the code when i'm at home.