When I speak L2 or L3, I say sometimes some words from the other languages that I know. I also have seen many people who have the same issue, they speak in English in some conference for example and then suddenly they say some words from French. What is the most effective way to avoid this or at least minimize its effect on our language speaking?
Edit:
Like I have already said, my question is more about this issue when we speak, and not with the whole language skills, and I agree that this happens a lot from the languages that we know better to the languages that we know less, but it might also happen in the other case, I mentioned this in the comments below though.