I just made quick check on SESTO SESNO 2 driver and looks like it use similar commands and principes. So it shold be much easier then I think.
I will try to adopt it this weekened.

All the parsing procedures and communication protocols already there I just need to dig deeper and make some changes.

So I think there no need to implement openweathermap JSON parsing features. And probably it is not a JSON it just looks like it. I am not an engeneer at all so can make such mistakes.