p.s.

Designating specific languages to specific users (So they will not be able to change other languages).

Today I've noticed that I can translate the survey, even if I don't have the language in the "additional languages":
https://manual.limesurvey.org/images/a/a5/Multilinguar_survey_-_add_additional_language.png

A week ago I had also added "Portuguese (Brazil)" for translation.
The translator started translating it.

Then I deleted the language from the "additional languages" box (didn't know when the translator would have time to translate).
After couple of days he told me he started to translate.
Now I saw the "Portuguese (Brazil)" translation is not in the "additional languages" but still we can continue translating the survey to "Portuguese (Brazil)", without the users seeing an option to choose "Portuguese (Brazil) before we finish translating".

Is this a "good bug" or that is how the feature suppose to act?

But still if a user adds this "?lang=pt-BR" after the survey number, he can still see the translation.

Or change the language of the site to "Portuguese (Brazil)", he will see "Portuguese (Brazil)" in the survey.