Sam uses an internet search engine to translate German into English. The German text shown is just a bad word-by-word translation of the English text, though Sam supposedly copied it from a book written by a German native speaker.
Sam states that nobody has been in the Men of Letters' headquarters for 65-70 years - despite this, the place is immaculate and there is no dust on any of the furniture.
The opening scene takes place in 1944 but shows a very recent Jeep (Wrangler in US) painted to look like a German military vehicle.
The payphone used at approximately 10 mins is indicative of payphones used in Canada and not the USA.