Human languages? I don't actually know it for a fact, but probably not. Most Americans take 2 years of French or Spanish in high school, and if they go to college for a liberal arts degree, then another two years of French or Spanish. Assuming you take the same language for all four years but don't do any significant extra-curricular study, this gets you just about enough of one language to get by on the day to day basics (asking directions, making a reservation, discussing the weather, etc.)
Assuming you don't then use the language regularly, within a few years, you'll have no functional knowledge of any foreign language. That is normally the case, and was almost certainly the case for Bill Gates -- I don't know when, with his personal history, he could possibly have had time or opportunity to use a language.
Re-learning is easier than learning, and in the years since he stopped being the CEO of Microsoft he's had time to do what he wants, but I've never heard that that involves foreign languages. I mean, he's a smart guy, and apparently enjoys reading, so I suppose anything is possible. Maybe he learned some Italian so he could read his original da Vinci manuscripts... but probably not.