"The intelligent cat only speaks French."
Translation:Älykäs kissa puhuu vain ranskaa.
In "puhuu vain ranskaa", the "vain" modifies "ranskaa". This means that the cat can't speak any other languages. In "vain puhuu ranskaa", the "vain" modifies "puhuu". This means that the cat can speak French but is not able to write in French. Also, the cat may be able to speak other languages as well.