The number of languages is certainly finite, but that doesn't mean Google knows all of them.
A quick search reveals that there are currently about 6700 active spoken languages in the world. (Granted, not all of them are spoken by people outside of tribes, and not all of them are written languages, but there are still hundreds if not thousands of written languages.)
Also, it's worth mentioning that a lot of languages with non-latin writing (e.g. chinese, japanese, persian, arabic, hindi, urdu) are commonly written using latin transliteration. e.g. for a persian speaker to write in native persian, he needs a persian-enabled keyboard layout, right-to-left writing support in the OS, browser, editor, and unicode support in everything as well. Because they can't always find that perfect combination, sometimes they just sound it out using english letters. Because there is no standard for this, there is no official spelling either, so anything goes.
Therefore, I seriously doubt that Google can claim to understand all written languages in the world. The question is, what does it do when it encounters something it doesn't understand?