It's German, -er and -e are pronounced like the Brits would, which is backwards for Americans.
When I go to dict.cc and listen to the recordings,
-er sounds more like I'd pronounce -e, and
-e sounds like I'd pronounce -er.
I speak standard educated American English.
Don't know if someone more knowledgeable than me has answered you during the year, but it is because 'wofur' (I really couldn't be bothered to search out a character 'u' with the umlaut) keeps the noun in the nominative rather than the accusative which would require 'der' to 'den' as you evidently know.
Ending a sentence with a preposition is perfectly fine, as long as you actually end a complete thought.
You're right. I was referring to the preposition rule, and someone above ^ linked to a source that states it's perfectly fine. When I was going through school in America, it was always taught to us that ending sentences with prepositions was "improper," so that's why I thought it was incorrect! And I never really questioned it because 1) it made perfect sense and 2) most English speakers speak English incorrectly anyway, so I didn't even bat an eyelash when I was introduced to yet another mistake we make.
But, okay, it's not a mistake. :) I see this now.