I like the house rule set forth by Babayaga. Language is already one of the least useful abilities, it doesn't need to be the most expensive, too. I like the idea of specialties, because when we learn new languages we still have our knowledge of linguistics to back that up, and rarely have to start from scratch, unless the language uses a different morphology, such as isolating vs. agglutinating languages.
As Narrator, you decide how much in-game training equates to a single rank, be it the ability or a specialty. Nothing says it doesn't have to take just as much time and effort as it does now. Polyglot should be reserved for characters who don't need to train to pick up a language, it shouldn't be practically required just to have a character who knows multiple languages.
I think what is just as necessary are some rules for multilingualism; perhaps "Native Language" should refer to all languages the character learned to fluency as a child, which would be limited by where they were raised.