I am a member of the German translation team.
When we file bugs about translatable strings on the GitLab/GitHub pages of the project in question, we post a link to it in the DL discussion, so that other translators in the team can have a look and know that there is a problem with the current state of the translation. See here:
When clicking on the link, it currently opens in the same tab. IMO, this is not optimal, since one might switch back and forth between the DL discussion and the Issue report to refer back to what other translators have to say. Opening external links in a new tab by default simplifies that workflow.
On top of that, I think it “feels right” to open links with a different domain name (l10n.gnome.org vs. gitlab.gnome.org or even www.github.com) in their own tab.
What do others think of this? Please respond to this question over on GitLab if possible (posting here for visibility only):