However, that doesn't help the OP and doesn't change the fact that there is not a big range of easily accessible English-speaking services
You don't need a "Big Range", you only need one school. Be it one with a classroom of 10 seats or one with 50. They both do the same thing.
The OP is going to have to do their own research on whats avail. If they really wanted to they could lookup the phone # of the DL office on
Spangdahlem and ask them where they send people. You don't have to be in the military to ask/get answers to that question..
Just to prove a point here are some Driving schools in Trier that teach in English. Amazing what a 15 second Google search can find..
Fahrschule Sauer & Müller - Roonstraße 1 - 54292 Trier
Fahrschule Daubenfeld - Porta-Nigra-Platz 5 - 54292 Trier- Tel. 0651/25758
Fahrschule Haas in Trier - Kaiserstr. 3a - 54290 - Trier - 0651/72125
And if for some reason they can't help you, I'm sure they will know of some others schools that can.