Check out this Wiktionary page:
https://en.wiktionary.org/wiki/Wikti...requency_lists
I find two language proficiency test lists that can be converted to difficulty list, they happen to group the words by difficulty to four or five levels:
Chinese:
https://en.wiktionary.org/wiki/Appen...Mandarin_words
Japanese:
https://en.wiktionary.org/wiki/Appendix:JLPT
The page doesn't have any Spanish test list, it has some frequency lists but again it's kind hard to set difficulty value based on their frequencies.
Edit:
For Chinese data, I found an excellent Excel file from a link in the TOCFL website(
https://tocfl.edu.tw/index.php/teach/download):
https://coct.naer.edu.tw/download/tech_report/