He translated the Bible from Latin to German in a language that people spoke so they could understand the Bible at all.

As far as know, the Swiss German dialects are varieties of the German language spoken from the late Middle Ages until the middle of the 17th century. These varieties are usually referred to as Middle High German (Mittelhochdeutsch) and as in all languages, there are words taken from other languages, which includes Yiddish for sure because of the long Jewish history in Europe.