Alessio, as I wrote once before, there is some mix upt with language tags.
I finaly figure it out :-)
If you look at for example: A Simple Card html you will find these tags for original language: _TMOVIE_LANGUAGE_ : _MOVIE_LANGUAGE_ .This tags is on all cards as original language.
Since XMM 5, _MOVIE_LANGUAGE_ imports MEDIA language and not ORIGINAL language. Same as _MOVIE_LANGUAGEENCODED_
The best example is the Brixie mod v1.0, where you can see both tags. Try set Media language to something else, and you will see the difference. I had to change my Movie cards from _MOVIE_LANGUAGE_ to _MOVIE_ORIGINALLANGUAGE_ to import the correct language