Bruno,
I have been able to tweak the environment and build gettext and libintl. With the updated libintl and environment, GCC reliably does not use NLS.
The issue is that libintl utilizes pthreads. AIX does not provide no-op pthread stubs in libc. pthreads is an explicit multilib on AIX.
It is great that gettext and libintl can be built thread-safe, but GCC (cc1, gcov, etc.) are not pthreads applications and are not built with pthreads. Because libintl defaults to pthreads enabled, NLS cannot function in GCC on AIX by default. The GCC included gettext was built in the default for GCC libraries, which was not pthreads enabled.
I can rebuild libintl with --disable-pthreads and I will see if that works, but the default, distributed libintl library will not allow GCC to be built with NLS enabled. And, no, GCC on AIX should not be forced to build with pthreads.
This is a regression in NLS support in GCC.
Thanks, David