i18n brokenness of C++

[Bonzini]

I restarted working on the Italian translation and found that a lot of error
messages are quite broken in the C++ front-end.  About every occurrence of
%s means that `class', `type', `declaration', `member' or something like
that is interpolated without translation.  I volunteer to fix these like I
did with the C front-end last year (which was much less broken, however).

Is an assign.changes paper needed to do these changes (which are mostly
boilerplate, but not irrelevant)?  If a paper is on the way, can they be
committed before rms signs it (which usually takes a month or more)?

Paolo Bonzini