[REVIEW 3-6][REVIEW 3-6] ~ appears in German unix OK/Cancel translations

In 3.5.7 the German unix OK/Cancel translations visually have ~ in them.

~ is our accelerator code, and in the last update of the 3.5.7 .de
translations ~ appears in the .de translations, but we have some unix
specific code which prepends ~ to the OK/Cancel translations, resulting
in a double ~

https://bugs.freedesktop.org/show_bug.cgi?id=56281

proposing 920807d4491834cd88e545fdb930c9105d58c4cd for 3-6 and 3-5 to
protect against this.

I'm unsure, reading the comments in the weird vcl code, if there might
be an additional problem under windows. If someone could check the
windows German 3.5.7 for problems in OK/Cancel that'd be good, to know
if we need tooling to disallow ~ in OK/Cancel translations. Or if we can
remove the platform conditionality.

C.