FIX: "staff" and "admin" wasn't translatable in site settings (PR #13204)

It also replaces the concatenated string with a translation.

GitHub

I think a test here will help prevent this from regressing in the future.

I think a test here will help prevent this from regressing in the future.

Superseded by FIX: Don't store translated trust level names in anonymous cache by gschlager · Pull Request #13224 · discourse/discourse · GitHub which also adds the requested specs.