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Yes, you're right, prosinec is December.

Czech:
leden

Yuck. ;) I don't think so.
In fact, "червень" (and belorussian word, too) related to "червены" (in Russian -- "червонный"), e.g. "red".



Also, I don't think "вересень" is related to "вереск"...

You missed one more language: Belarussian (aka Belarusian, Belorussian) month names are also Slavonic, some are similar to Ukrainian.

1. translations: January: студзень [studzen] = cold
2....