Marianne80 - Have you updated the text key for messages.column.message-replies-count.label from studio > text editor?
Regarding the messages.column.message-replies-count.label@component:message-list string, this is for restrict the changes to the only message-list component.
If you will update messages.column.message-replies-count.label text key it will update this keys for the whole community. By adding @component:message-list it will be same for all other places.
Here is the document https://community.lithium.com/t5/FAQs-email-templates-and-text/Set-the-scope-of-a-text-key/ta-p/109017.
