That’s right, it should work, they must be identical.
You still got results in both languages or is it something else?
Does it work if you switch to the “Regular engine” instead of the “index table engine” on the search options panel?
I may have 1 more trick to try, but I honestly have no clue at this point what exactly is wrong. I feel like there are missing translation ID’s are causing the mystery, as I can’t think of any other possibility here.