It's possible to change the metadata of a book with the mobi2mobi perl script (which also has a GUI... just search on the forum)
If you change it to spanish, the kindle will choose a spanish dictionary for translation (no matter what the primary dictionary is set to be) and so on
there is a thread about this stuff (a lot of the stuff on the beginning outdated with the new fw updates)
https://www.mobileread.com/forums/showthread.php?t=60103