I am Italian, I live abroad and mostly speak English since ~8 years. The "issue" I face is that the dialect version of my Italian feels easier and easier, but I believe I still kept a good written version of the language. Few years back I spent 1 year in Spain - I had serious issues communicating in Italian during that time. I think as long as your foreign language is very different, you are good, if it's similar, not so much.

Edit. Ok, to tell the truth, I don't feel very compelled to maintain a good spoken Italian. On the other hand, I do want to keep my written version as sharp as possible.