Because the Peacock Sky has so many worlds mashed into one, they have multiple “common” languages.
Starting “common” languages include these:
Vestyx, Thulia, Nomina, Kieros, Kondarr, Barev, Sorn, and Gazrin
Racial languages also exist, and often work as “code” languages when out in the world. For instance, most people may not know Monkashii, so speaking in it amongst your party might confuse outside listeners.
Certain racial languages like Kobold, Gnomish, and Thulian are also very common due to the numbers or actions of their races. Kobolds have shown up on, at least in small numbers, on almost every shard due to their tendency for exploration and accidents. Similarly, one or two Thulian merchants can be found on any one shard, and often spread their language as a trade pidgin as well as translating for others.
Both Gnomish nations have spread out as well. If taking Gnomish, one must specialize in (grower) or (builder), though both can be taken as separate language slots. The specialization gives you a +2 to communication checks with the race specified, and a -2 on the others. Taking both languages removes both the bonus and the negative.