While in Nepal, my time is taken up with two different languages - Nepali, which I use to get by in life, and run a lot of the elicitation session in, and K. which is my target language of study. My experiences of, and with, these two language, has been rather different.
Nepali is the langauge in which I have some productive competence. That is, I can speak it - not fluently by any benchmark, but certainly enough. In K. however, stringing together two sentence is a task of great difficulty. It's a common phenomenon that linguists don't possess any fluency in the language they're studying. While there is a school of thought that emphasises learning to speak the langauge being studied, I find that, especially on this short trip, I'm stuggling to find time to document, let alone learn.
That doesn't mean that I have no competency in K. I have found I've developed relatively good intuitions about what's grammatical - often for reasons I haven't expicitly analysed yet. My competency in K. would definitely fall into a much more passive category than my Nepali.
Because the two languages operate in two very different parts of my brain, there is relatively little cross-linguistic interference. There are a few lexical domains where I've done extensive elicitations in K. that interfere with Nepali - I'm much better with K. body parts than Nepali - but on the whole I don't tend to get too confused between the two languages.
Unfortunately, between the two of them they've obliterated any Polish-speaking skills I had remaining.