No matter how long I search or reading docs, I cannot find a place how to create a localized blueprint.
What I mean is, either translate an existing blueprint (additional language than English), or create a new with several languages.
Is this currently not possible or am I missing some … ?
Good point. I’m working a lot with this NSPanel blueprint and it is a pain to keep it translated with all the translations.
It would be nice to have some translation engine for blueprints or if one could get translations strings from Home Assistant via a template, but as far as I know, this is not available. 
But why don’t you write this as a feature request?
Did not know how this is handled here … but made it right now: Localized Blueprints (translating existing)
Before I digg deeper into your code, how do you perfom this now (still a novice to HA, but I am learning … coming from a web developer world, and here are many things are handled in other ways …).
thx!
Sorry, just saw your message.
We have created a dict with all the strings. In our cases, not that many, but till a huge number of lines: https://github.com/Blackymas/NSPanel_HA_Blueprint/blob/d704de853a029197a2ca8fe9c8466edef0c277d8/nspanel_blueprint.yaml#L4175
Then we use mui[language][key] around the code.
The Blueprint inputs are still only in English, just the strings printed (in this case displayed in a screen) are translated.