If youre file has many stories, and you want to change the language for all of the stories, just choose 'find/change'.
Leave the 'find what' and 'change to' boxes empty.
In 'Search', choose 'document' or 'All Documents'.
Also leave the 'find format Settings' empty.
In the 'change format settings' box, choose 'Format...' > Advanced Character Formats' > Language.
Choose your language (i.e. French, I suppose...)
Now choose the button 'Change All'.
There you are.
Piece of cake, no?
Hope it helps.
L.L.