[Markoff]

The non descriptive names are better because they can be consistent across different countries not depending climate

July in Croatian - Srpanj August in Czech/Polish - Srpen/Sierpen

because for obvious reasons harvest time in Croatia is one month earlier than in Czechia

though your example for April in Polish makes no sense

April in Polish - Kwiecien May in Czech - Kveten

I'm pretty sure flowers are blooming (it's not about flowers, but about blooming) in Czechia earlier than in Poland, so the names should be reversed

though even English/German/Slovak months are not without their issues, October should be eight, November ninth, December tenth based on their Latin names, this video makes fun about it, but honestly I seriously like the proposed system:

https://youtube.com/watch?v=vunESk53r5U