do not show "copy in english" when using C as locale

Summary:
qlocale differentiates LANG=C from LANG=en_US for us it is
though as the native untranslated strings are english, so when
kinfocenter is invoked with C it will effectively be == en_US.
with that in mind we don't need the copy in english button when
using C.

BUG: 403368
FIXED-IN: 5.18.0

Test Plan: LANG=C.UTF-8 no longer causes the button to be visible

Reviewers: mart, ngraham

Reviewed By: mart, ngraham

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D26792