-
I used to go to Switzerland regularly. In the francophone regions when I tried to speak French people would either ignore me or reply in English. In the Germanic regions if I tried speaking in German they'd assume I was a lazy French Swiss who had never bothered to learn German and would reply to me in French.
-
Swiss German is as foreign a language to Germans as English.
Schwyzrdütsch occurs in several depths of accent. Some of it is quite close to standard German, but that from other regions is indeed completely unintelligible to a German German speaker. Then again, I can't understand a word of really heavy Platt (influenced by Friesisch), Schwäbisch, Bayrisch, or Österreichisch, either.
Reasons for my interest, in order of precedence.
I like the suggestion of doing a GCSE course to start with.