the demographics\statistics here in my location shows that when someone with DID has alters that speak a different language its because of that persons cultural background\native languages and the result of alters being in control during foreign language classes or self taught through things like watching movies, books, tv shows...

example some of my alters spoke Spanish and French from watching sesame street and other PBS\documentary shows. some spoke native american (my cultural background) all could speak English (because I was raised here in america and the american language is English) some of my alters could speak german and french from high school classes, I even had an alter that could speak a mixed up version of languages that was learned from watching school films and PBS films on other cultures. I also had an alter that made up their own language like normal children do when they are small.