Gary,
I tend to Marmorstein's etymology of the Deutch surname. It appears that
Jews in large numbers began moving East >from Central and Eastern Germany
ever since the end of the 11th century (the 1st Crusade). Many Jews
probably emigrated to the kingdoms of Hungary and Bohemia and the
borderlands of Silesia in the 12th and 13th centuries along with Saxon
German miners invited by local rulers to develop mining industries in their
respective domains. German speech (These Eastern German Jews probably
spoke German or Judeo-German and not Yiddish) was not an especially
distinctive feature of these Medieval Jewish immigrants. Deutch like
Friedlander, Venetianer, and Hamburger was more likely a cognomen that
described the origins of an individual or family that eventually was adopted
as a surname for the lineage. Cliff Geertz shows in his ethnographic
reports on Moroccan social practices that while Arabs and Jews traditionally
identify their family allegiances by lineage rather than by surname the
communities they live in often assign them names describing their origins,
callings or other characteristics. These are often "inherited" by their
offspring and eventually become a permanent part of the names of entire
families and lineages. It is most likely that the surname Deutch and
Deutchlander was the end product of such a process.