Can’t translate ticket list headers

I can’t seem to translate the ticket list headers. We are a multilingual website, but the current headers only show the german translation in all languages. I can’t find the custimization option to the headers and can’t find any entries in the string translations.

Our site is running WordPress 5.53 (but the problem is also active on our local test server with WordPress 5.6)
The support plug-in is version 2.1.9
PHP version: 7.1.25