as a beginner I looked a lot into what design decisions went into the Flow Hive, etc. And after reading up on Langstroth frames I understood that most parts of the world use these.
What I missed is that us Germans always do things differently, so most of the beekeepers here seem to use DNM (Deutsches NormalMaß - “German Standard Size”) frames which seem to be a lot smaller.
Now I am not sure how to get my first colony if everybody around me only sells DNM.
Are there best practices on how to move bees from one type of frame to another?
You could see if packages are available and start there. If getting a colony with DNM frames is the way you want to go then really all you need to do is figure out a way for the top bar to hang from the inner edge of the langstroth box (maybe just attach a langstroth frame top bar to the top of the Dnm frame. The bees will build comb outside of the DNM frame but that’s ok as long as you have the frames together it should work out ok.
You can put regular deep langstroth frames in between and cycle the Dnm frames out over time.
Alternatively, if those Dnm frames are foundationless, you could cut the comb out and rubber band the comb into langstroth frames but that kind of comb surgery might be intimidating for a beginner.
Dadant Mod (US) 10-Frame has about 20% market share in Germany, meaning it is easy to find Dadant Splits or NUCs for the bees. Crucially Dadant Mod (US) is 100% compatible with Langstroth, they have identical inner and outer measurements, only varying in depth. Thus a Dadant mod (US) for the brood with a Langstroth standard full size (deep) as a super allows you to use Flow frames in the standard Langstroth super.