In a thread on AH.com about the Modern Bundeswehr ending up in 1941 Germany there is this back and forth about accents.
There's also subterfuge, if they play their cards right, they could pretend to be from a NAZI victorious Germany.
"This is General Hans from the (etc.) Panzer Division to Herr Furher, I invite you to come see zee wunder weapons that you and your successors are responsible for in the Great German Reich of the 21st Century!"
"Ok, now remember, wait until he is in the middle of the camp, THEN we strike"
In the Nazi future, Germans speak with a German accent even when they're speaking German...