I am going to assume that vegan options would be acceptable to you both, so here goes....... We were in Berlin for three weeks in June 2018. While we cook most of our own meals, owing to both personal choice and budget, we did go out more than usual in Berlin, as there were some delightful options. I will also add that we don't do fancy meals and eat our largest one at mid-day.
The food court at the Mall of Berlin has veg/vegan friendly options. As we live in a falafel wasteland (borrowing from Pam in Idaho), that's an option we always search out. We found a good one in the mall, Boussi: https://www.mallofberlin.de/en/stores/boussi There were also quite a number of other places at which we could have eaten, but we discovered that after we were full. We did go to Boussi twice, the mall is air-conditioned and it was hot. :-) One interesting place had potatoes that were riced and topped with your choice from a generous list.
We like Indian food, which can most definitely be veg-friendly. Often times there are daily specials, which is nice. We enjoyed this one: http://veggievega.berlin/ I got the daily thali plate, Denis got a jackfruit curry plate. It was rather far from our apartment, or we would've gone again.
We went to the RS recommended Chutnify, which was edible but meh.
We got good dosa plates at Satyam: http://www.mysatyam.de/ They also have a Sunday buffet.
We did find a place to try a setitan based vegan doner. It was, um, trying to be polite here, underwhelming. Nope, it was just plain awful. And so not worth the trip there and back.
Japanese is not, in our experience, really veg-friendly. We found a delightful exception in the vegan restaurant Ryong: http://ryong.de/ That's one I definitely could have repeated.
Vietnamese is not something we've ever had. We went to Vegi-rou twice: http://vegi-rou.de/
There are also prepared options at outdoor markets. We found the Turkish Market a lot of fun. And who doesn't find fresh baked flat breads comforting? And speaking of breads, hearty German breads make delightful partners to salads composed of market fresh ingredients, especially when it's hot outside.
There were lots of other options on our list that we just never got to. As Jo says, check Happy Cow. And thanks for the food memories, as I had to go look back at my journal. Now I'm hungry though. ;-)
Donna