In the US, translations are an original copyrighted work, not a derivative copyrighted work.
That said, the Fedora FPCA is different from most CLAs, in that its sole purpose is to ensure that Fedora has permission to use contributions without an explicit license under a Free license (MIT for code, CC-BY-SA for content). If a contribution is made with a different Free license (e.g. same as the upstream), Fedora uses that licensing.
So, lets step through the process:
= No explicit license =
1. A Fedora contributor makes translation changes and contributes their changes to Fedora, without indicating a license.
2. The Fedora FPCA says that Fedora (and anyone who receives that contribution from Fedora) can use that change under CC-BY-SA (I'm guessing that translations count as content).
3. The upstream can take the changes from Fedora under CC-BY-SA.
OR
= Explicit license =
1. A Fedora contributor makes translation changes and contributes their changes to Fedora under a specific license (e.g. BSD, because that is what upstream uses).
2. Fedora takes those contributions under the BSD license. (The FPCA permits this, as long as the license is acceptable for Fedora, aka, a Free license.)
3. The upstream can take the changes from Fedora under BSD.
Does that help?
Tom