After the upgrade to KDE Plasma 5.3 on Tumbleweed last week, KDE desktop 5.3 is
shown in English, although set to a different language in 'configure desktop',
'configure KDE 4 applications' and in Yast's 'Language'. The panel, the
application launcher, application menu, witgets, etc. are in English. On the
other hand, Dolphin, Yast, Firefox, Libreoffice and other applications show in
the correct locale. 
I have checked if the localization exists for my locale, I mean, that Plasma 5
is translated to it and it is. Kaos Linux, for instance, uses the same Plasma
5.3 and the same version of language packs installed on Tumbleweed (kde-l10n 
15.04.1-1.1) and the panel and widgets are ok.
I have seen this with another locale, such as Spanish.
Could it be a configuration issue?
Thanks for your attention.