0. use Quizlet's search to find large collections of vocabulary:

1. search for e.g. french (https://quizlet.com/subject/french-basic-vocabulary/)

2. look for the list(s) with the most words

3. check quality (if you can :)

4. copy them to your language directory

5. repeat

if you speak German, the addition of "Langenscheidt" could help...

Example (contains about 6000 words): https://quizlet.com/ThomasBisig/folders/franzosisch-wortscha...

I think for some languages this might be problematic. I am trying to learn some Russian and the word endings changes based on how each word interacts with other words.

For example :

"I know" : Ya znayu

"We know" : My Znayem

"He/She Know" : on znayet/ona znayet

"You know" : Ty Znayesh

"They know" : Oni znayut

etc

Knowing that 'znat' means 'To know' might not be enough to place a word in a sentence

Some suggest that it might be better to memorize sentences or phrases instead

Finnish is similar with the various suffixes based on context. The rules are reasonably regular, and in a classroom with a list I can make the right choices.

Doing it in real-time when speaking is more of a challenge though.

Exam syllabuses often list them. eg search for GCSE French syllabus (UK exam) and I think you'll find a list of around 5000

This is awesome !

Any flashcard system will have shared decks of the most common words.