I've thought first person games could be useful for self improvement in lots of other ways too. Such as getting comfortable with public speaking, or social anxiety in general.

For language learning, this might sound silly, but I've also thought a first person role playing game where you're a baby and everyone speaks to you like they do to babies in the language you're trying to learn. (My pet theory is that children aren't necessarily way better at learning language, but it's more how people interact with them: speaking slowly, using small words, telling them what they're doing, etc.