askchapo

Depends entirely on where in Europe you're going - There are technically more countries where you'll be able to use German, but it's often limited to specific areas of them that are right next to Germany, so neither language is super useful for Europe in general.
You'll have better results working on your feelings of being a dipshit who only knows one language - even if you learn a new one you aren't going to be speaking the local language for a lot of the trip, but the locals will probably speak some English, so you'll be doing a lot of communication with a mix of that and a translator app. Plenty of locals won't speak any English though, or any other foreign languages, because like you they don't have a need for a second language; neither you nor they are dipshits for not knowing how something you have never needed or used works.