Here are links to the 1000 most frequently used words in French, German, Spanish, Italian and English.
I'm offering them, not to suggest that pupils be given them to learn as blocks, but as bases that we need to touch frequently in our teaching from the early stages. There are further core vocabulary lists in two out of the three examination board specifications for GCSE.
AQA vocabulary for GCSE French is included in the subject specification, here
Edexcel spec includes a minumum core vocab list, here
OCR spec does not appear to include a vocab list, but is here.