Comment # 6 on bug 1118870 from Wolfgang Bauer

(In reply to Stephan van den Akker from comment #5)
> This workaround indeed makes the error message of K3b and locale go away.
> And all the ripped files are now read by Amarok.

Good.

It's not really a bug then (not in k3b anyway).

The problem is that you configured en_NL (for Currency), but there is no locale
with that name. (somebody tried to push it to glibc a while ago, but it was
rejected: https://sourceware.org/bugzilla/show_bug.cgi?id=14085)

Of course, Plasma's locale settings better should not offer you unavailable/not
installed locales in the first place, but there's already bug#1015858 about
that.