Version: 2.4-GIT (using Devel)
The settings dialogs of plasma applets within amarok are not translated because the libplasma catalog is not loaded.
I do not know whether it has to be loaded manually by amarok or should be loaded automatically since other plasma applets on workspace do not show this problem and are translated.
See the problem here:
As I mentioned on #kde-devel and in bug 254481 (in an abstract way) it is devs part asking i18n people (email@example.com or #kde-i18n).
I can reproduce it on 3 systems.
I can confirm this on Arch Linux:
*** This bug has been marked as a duplicate of bug 255971 ***