@EarlBird said:
Correction of bad machine translation?
The movie Black Sea has a terrible Swedish translation which is obviously machine translated.
May I add a different but correct Swedish translation instead?
What is the TMDB rules for these scenarios when someone has added something that other wants to change?

I assume you are talking about this movie.
http://www.spcrystal.com/movie/246080-black-sea
If I got the movie right, then...

I believe the text was added by a user who has not logged in for over 4 years.
I don't see a problem if it's your native language and you encounter errors.
Yes, I believe you can make corrections or add new text without any problems.

Yes, that's the movie and Swedish is my native language. Hence I reacted on the awful grammar. I will update it to something better.