After while of nothing happening, we received a donation! This was enough to get motivated again and we added lots of new features! You can translate the calendar now on Weblate and it is available in many more languages.
One of my favorites is the community engagement: I asked on Mastodon if the open-web-calendar can be translated to Welsh and someone responded. Many more translations followed Welsh: Norwegian, German, Croatian, Polish, ... . 
All translations turn up live after a few hours. I hope this is a rewarding contribution process.

So, thanks for the donations and it is really a good place to leave your money from my perspective :)