Language Barriers by Frank's TS4 Mods
Five languages for your sims to learn: Selvadoradian, Windenburgish, Toki Sulani, Sixami, and Simlish.
Native languages are assigned to sims (children and older) depending on their home world, traits, and occult type.
Toddlers will acquire their native language(s) once they become children. The languages they acquire depends on which ones they have been exposed to while growing up.
Sims can learn another language by using Simlingo, reading a textbook, or interacting with other sims who speak it.
Communication between sims is limited when they do not share a language. New interactions unlock as you learn more of the other sim's language(s).
Sims may miscommunicate when they do not share a language. This results in an embarrassed, angry, or tense moodlet that will get worse the more they talk.