Every time I have learned a new language, it has affected the ones I already knew. French altered my German, but then my college German reasserted dominance over my French.
Then there was Hebrew, which made it so that I couldn't construct a thought in German without Hebrew interference. My Hebrew was diminished by time and then a bit of Arabic and Russian. And finally, it is Estonian at the forefront of my linguistic brain.
That has never really been a problem. The last language I studied was the language I needed to use.
Here of course, there are Estonian and Russian speakers. I know very little Russian, but I do try to at least exchange pleasantries with those who speak only that language.
Add into this mix my orthodox Jewish neighbors, who speak as far as I can tell only Hebrew (except the husband, who has some English).
So yesterday, I spoke Hebrew to my neighbors, Russian to the cleaning lady, and then Estonian to another neighbor in the space of like five minutes.
And my brain cramped.
Suddenly I was questioning whether I was using Hebrew in my Estonian (ma is I in Estonian and what in Hebrew, and as I used it in Estonian, properly, I second guessed whether that actually did mean I!). Who knows what I did with the Hebrew and Russian. Okay, I do know there was some Estonian in the Hebrew (the wife asked if I was American and I said yes in Estonian).
So this is a new linguistic challenge for me. Try to work with two languages I have an okay command of and one I know pleasantries in without having them interfere with one another.
It is either really going to make my brain work better or shut it down completely.