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: