According to a few dictionaries I checked, int is an abbreviation for numerous words such as international and internal. vim considers it "local" or "regional."
For me, int is in the main vim listed by :spellinfo;
You can see this using :spelldump which says int/13, meaning it is ...
Thanks to @D. Ben Knoble's comment I was able to see the source of the issue:
Warning: Cannot find word list "eng.utf-8.spl" or "eng.ascii.spl"
To solve the problem:
I looked for the files locally
which gave me these results:
Then copied ...