[DanCooper]

The source languge setting is only for new movies/tv shows. After changed the source language you also have to select all movies and tv shows in your list and set the language via context menu to that language you want.  

Thank you Dan.
I will immediately try as you say.  

I tried deleting one film, deleting also all the files in the folder, renaming the avi file.
Then I clicked on Update Library.
The system found the new file. I clicked on it and pressed CTRL+I
The file was correctly scraped but still in English   
Plot in English and Title in English. 

Please check if the correct language for this movie is set (Context menu => Change Language, the correct language should already been pre-selected).
Please check that you've enabled a scraper that supports multi language (TMDb for movies, because IMDb is english only and all other scrapers are german only).
Please check that the TMDb scraper is on the top of the list.
Please check that your language is available for this movie on TMDb.