Add a regression test to verify that NLS translation works.
We've never actually had a formal test for this facility. It seems worth adding one now, mainly because we are starting to depend on gettext() being able to handle the PRI* macros from <inttypes.h>, and it's not all that certain that that works everywhere. So the test goes to a bit of effort to check all the PRI* macros we are likely to use.
(This effort has indeed found one problem already, now fixed in commit f8715ec86.)
I noticed couple of buildfarm failures on bumblebee and akepa.
