@Maria, I think almost the same about the thought process: even when there is some kind of language, it's usually just scraps of sentences or individual words* that work as crutches helping you think more quickly or/and smoothly. But when you're writing or speaking (or thinking about writing or saying something), it's a different story because then you are focusing on a particular language and you're kind of translating you thoughts into that language. That's why I find the idea of linguistic relativity so interesting: even if we don't think in sentences, it doesn't mean that language doesn't affect our world view at all. 

*Though I actually suspect that it's not a universal rule. For example, a friend of mine says that she does subvocalise her thoughts properly, and it's like having a constant inner monologue or even dialogue. I find it hard to imagine, but I have no reason not to believe her.

I'm not really sure about it, but I don't think that communication in my dreams is normally conducted through the medium of any specific language. Sometimes (most of the time? I don't know really) we think in concepts, not in words or sentences, and I suspect that in my dreams reactions, events, feelings and abstracts are the main language because there's no need to narrate what I am imagining. So the only dreams in a foreign language I remember were dreams about making mistakes, not being understood or not being able to string two words together. The worst was about English: I was talking with someone, and in the middle of the conversation I "realised" that I actually can't speak English at all and therefore can't answer any question. Not pleasant, so I would rather have language-less dreams, frankly. 

@Kseniia

Your description of your dreams as being conducted through "concepts" is how I feel when people talk about thinking in a foreign language. I believe, generally speaking, thoughts are rarely had through "full sentence" so it is difficult to say you think in a particular language. I think you can start constructing the sentences that you are about to speak or write in your thoughts in a foreign/native language, however generally I feel thoughts are not sentence based, so they are rarely language specific.

I do recall however dreaming in a foreign language (where there is "dialogue"). I can even recall specific words and grammar used.