All "romance" languages tend to have similarities that allow you to functionally understand them all if you have a very strong grasp of another. Don't get me wrong, I don't mean to imply that fluency in one is fluency in all. But you can pick out words here and there and, on occasion, figure out what is being said based on context.

I'm not fluent in Spanish, but I do have a strong grasp of it. As a result, I've found myself able to piece together stuff being said in Portuguese, French, and Italian. Enough to get by, at least.