I've had some troubles with languages and translations - My situation is as follow:
- I'm German
- My Computer OS is German
- My Odoo is Italian (as default language & user)
- My translated languages are italian, english, german and russian.

Some problems I have:
- On the website, default language is selected by browser language, it is impossibile to set default on all, some pop-ups are still german
- while translating text and products, some time I see all 4 languages, sometime I see only 3 and source
- often I have duplicated language values in the translation, see below: