It varies from language to language, but those word lists are all around. https://en.wiktionary.org/wiki/Wiktionary:Frequency_lists is a good place to start.

I am not a believer in rote word memorization, but rather putting each word in a sentence and using the sentence as the memorization route. Rote memorization stores the word in a different part of the brain than the language center, and using the sentence as the unit of flash card seems to override this.

I still see use for flash cards to re-trigger words in memory, but not for actually learning new words. I can't tell you how much I struggled to de-link certain words because I "memorized" them at the same time and so mixed up the meanings of the two words.