The Louis/Lewis name fluidity is not just confined to Jewish populations.  My GGgrandfather was born 1828 in the middle of Pennsylvania, 2 generations from Alsace ancestry.  This is an area where German language hung on long after Louis was born.  His profession was a farmer who made custom cabinetry.  When he dealt with English speakers he was Lewis and when his customer was a German speaker he was Louis.  He was fluent in both languages.  The wives in this line weren't fluent in English until 1900 when the sons married out of the community.  I have documents where he uses Louis and Lewis interchangably.