FileBot

Is it possible to add the spoken language to filename?

example: renaming some french movie to "movie's title, french or france or fr"

I mean the video file, not the subtitles. just to be clear.

Yes.

There's some people that did at and there's some format expressions in the forums, though might be hard to find sometimes.

You have two options:

1. MediaInfo from File => Use {audios} to grab info from the container metadata (naturally only works for mkv/mp4)
2. Extended Info from TheMovieDB => Use {info} to grab full info

This might help:
http://www.filebot.net/forums/viewtopic.php?f=8&t=1038