Hi @ivo, regarding donations, I would recommend leveraging existing facilities and frameworks such as:
Players such as these already handle all of the security and compliance aspects of handling credit/payment cards. I think all of them handle a wide collection of countries and languages.
I think the implementation with windy.com would be windy-specific rather than some new open source project. But perhaps I'm not looking at it the same way you are.
I'm willing to help any way I can. I've used stripe in my own project - so I have some first-hand knowledge there; and have some prior experience with paypal and patreon - although as as standalone services.