Sounds like a disorder relating to MPD, but it could be any number of things. My advice is to be supportive as much as you can be, when ones own mind is the issue it just feels impossible to deal with.
Not all disorders are ones that will affect work in “predictable” ways, everyone is different. They might just like practicing dialects and not have particularly strong social and coping skills.
As difficult as it can be to interact with people like that, keep in mind their perspective: it might feel like everyone wants to alienate them which makes it difficult to interact without that assumption tainting the experience.