If you must speak Yiddish to trade diamonds in Antwerp, Swiss German is the language to master in Switzerland. Not that the Swiss do not speak German or English. They do, and usually very well. But the Swiss Germans are so fond of their language that if another Swiss addresses them in High German, they are likely either to switch to another language or answer in Swiss German. Of course, like all Swiss, they also enjoy showing off their English to foreigners and if you begin in English, asking if they speak it, they will probably be glad to oblige. To truly belong, however, you really ought to speak Swiss German. If you only speak English and it is apparent that you are a foreigner, the story is different, as people will be proud to show off their language skills.