There are many languages of Iona. You start off knowing one language from your country of origin. If you are not from the Arkhosian Empire, you also start knowing Common.
Each language is arranged in a language family. When someone speaks a language that shares in the same language family as a language you are fluent in, you can make a moderate skill check equal to your wisdom modifier + one half your level. If you succeed, You understand the gist of what was said, but you lack the subtle nuances of the phrasing or implications (This is similar to knowing English and kind of understanding Spanish or French—it’s not a perfect fit, but you can figure out key words and decipher the most basic meaning, if nothing else).
*These languages can only be learned if your character is from those countries, or if you have a good roleplay reason as to why your character would know a language from a closed, insular country that does not export its culture.