The funny thing is that other Slavic countries use similar names but some are moved 1 month back or forth because flowers bloom earlier/later there :)
And days of the week are simply numered starting with sunday = "niedziela" (not working day), "poniedziałek" (after not working day), "wtorek" (secondary day), "środa" (middle day), "czwartek" (fourth day), "piątek" (fifth day) and "sobota" (sabbath).
I never remember the names of the roman months and have to count them starting from january.