After a few times using DeepL, it will return "Unexpected token '<', "<!DOCTYPE "... is not valid JSON", likely hitting CloudFare bot protection or too many requests.
If there is a way to integrate DeepLx (forked version of DeepL Pro API), I imagine it will work. I tried altering the Javascript file to use a local docker container I set up with DeepLx, but I couldn't get it to work, since I'm pretty inexperienced with coding in general.