Assalamu Alaikum,
Well, if you speak more than one language, you will probably have some issues when speaking each simply because they are competing in your brain. I've learned 4 languages, and even though English is my strongest language, I sometimes will forget a very simple word in English but remember it in another language. Also if you're not using a language often, even if you can understand it, you will have difficulty speaking it because it's not your main use of communication. However, if you go to Pakistan for example, and no one there speaks English, and you're forced to speak Urdu to everyone, then you will actually pick it up very quickly and it will become much stronger than before. It's all about the circumstances you find yourself in, but the simple rule goes, "if you don't use it, you'll lose it!"