Can not access https://subtitlestranslator.com

[torbjornljung]

I've specified this URL as OK, but Avast still blocks it, even after I clicked "Continue anyway",

[DavidR]

Only two hit on this check - https://www.virustotal.com/gui/url/6b91367077168231dfd045f4831f3821f1e9c8720d402a57f12ff6cc15b3aeb5 - there are multiple redirects and one of these could be implicated in the alert.
Some security issues reported here - https://en.internet.nl/site/subtitlestranslator.com/2238699/
Low Security Risk reported here - https://sitecheck.sucuri.net/results/subtitlestranslator.com - with some Hardening Improvements suggested.

These may or may not be why Avast is alerting - you can use the - Reporting a Possible False Positive File or Website - https://www.avast.com/false-positive-file-form.php.
You should get a response in a day or two.
This may or may not be what Avast is alerting for.