Tabs are good
Having persistently available tabs supports the idea of recognition over recall. It's theoretically harder for a user to forget language n when it's sitting right there in the UI.
But not here
Tabs should be relatively few in number (I like 3-7). Any control in too great a number can become noise and users will inadvertently block it from their mind. I may have my psych terms off here, but I attribute this to the intersection of cognitive load, Hicks Law, and a user's willingness to grant you their attention.
Finding a better solution
The challenge seems to be that you want to
- Allow a large number of language options
- Not present all translations simultaneously
- Encourage the user to complete all translations
- Make language switching convenient
How about a select box that allows the user to jump to a specific language, combined with a pagination-style switch to simple flippage through languages in sequence?
Side note:
Hopefully you are also internationalizing your own UI so these languages display in their localized rendering.