I hardly speak German and can use the IFE, so I presume it must be in English 🙂 If my memory serves, the IFE menu is actually available in more than 2 languages. Can’t remember though if subtitles on movies can be hidden or not.
The main issues with LH are the old business class seat (still equipping the majority of the fleet – B747-8 have the new one) that is the worst one among European airlines, and FRA, the worst hub in Europe.
Regarding your second question, you wrote “the evening before”, so less than 24 hours in FRA, right. If more this could be the explanation. And did you try several flights from ABZ? If the right booking class is not available on this leg, it would increase the price of the transatlantic flight.