Guess it is tied to the society skill and the multilingual skill feat as you said.
Then it is up to both the society rank and the multilingual feat.
You could take it 1 time and the increase your society rank to get more languages, or you could take the multilingual skill feat more times.
Eventually, both of them.
As a GM I would also allow regional languages through heritage like Hallit. Again as a GM adding a language to a background also seems fine. Also again GM fiat you could allow a character who is spending downtime learning to gain the language with enough time and successful skill checks.
|David knott 242|
Also note that the "bonus languages from high Int" include the ability score increase that you get every 5 levels, assuming that Int is one of the ability scores that you boost and get a higher mod from.