I don't think that there is such a difference from canton to canton as to render it impossible to understand the various dialects. Ok, there are words here and there, but you have that in any language. I think it is best to learn High German and keep it as official language and then adapt it a bit, this can even hide some mistakes. That's what my husband does, and he sounds quite good. Swiss German is a very versatile language, because you are allowed to make up words. I thought of a word the other day we used to use as children when you came in from the cold and your fingers really ached: "Kuehnaegle". I just can't find an English word for that!