There are many different French dialects, depending on where it's spoken, but for the most part they're all mutually understandable. If you learned French from a Parisian and then traveled to Montreal, you would still be able to use the language without much of a problem - though you might need to pick up new vocabulary and train your ear to hear it a little differently. It's similar to the regional accents you'll find within the US - think of how English is spoken in New York vs. Texas, for example - or how English differs depending on whether you're in Canada, England, or Australia.