I don’t think the Motty/Mordechai issue is relevant. Motty is not a Yiddish name; no one ever named their kid Motty at his bris, and Motty doesn’t mean anything in Yiddish. The word Mordechai, when pronounced with a heavy Yiddish accent, became Mudche, which evolved into Mottel and (the more American) Motty.
Yiddish names do have halachic ramifications, as many others have mentioned. The Kitzur wrote ???? ?? on the topic of names in Gittin, and he discusses Yiddish names in there too, IIRC. Many other Acharonim include Yiddish names in their Gittin analyses as well.
golfer – Regarding the Kaminetsky girl with the name Ettil, why don’t you ask them? I honestly don’t know enough (any) Kaminetsky girls, but maybe it’s a boys-only policy?
Sam2 – I know someone named Yedidyah and he’s not embarrassed of his name at all! His English name is Justin: We used to joke, “Yedidyah homework Justin time!”