I agree with Jdale and Wolfwood. I know a range of languages, but several I can only read - never had any resources to learn to speak them properly. I would also apply this to math, which is a language of symbols that we don't really pronounce.
For me as a GM, rather than a linguist, I would look at the type of character. If they're a scholar and can justify a lot of book-learning of the language, then written-only make sense. If the language is spoken around them at all, though, they should have at least a couple of ranks of spoken skill. Most civilians will have only spoken and no written, in fantasy/medieval cultures.