In the Bookmarks menu, the “Recently Bookmarked” folder synced its French profile translation into a German profile. - Steps to reproduce: sync a German and French Firefox profile. Notice that the French translation for “Recently Bookmarked” folder in the bookmarks menu sneaks its way into the German profile

This is "expected," though unfortunate, because Sync is not locale aware. As far as it's concerned, "Recently Bookmarked" is just another query whose title changed between the two devices. Sync also doesn't know that default bookmarks (bug 1177516) synced between two profiles in different locales are the same. I think Richard's suggestion in bug 1177516, comment 10 to make these default items virtual would fix this, but Places has no real notion of virtual bookmarks or queries yet. See also bug 1310295.