build: create and install .mo translation files

build: create and install .mo translation files

If --enable-translation was specified to configure, build and install
.mo files for the selected message language(s). The languages enabled
can be chosen with the --language-msg option; by default all available
ones will be installed. The .po source files for available languages
are seached under the po/ subdirectory; at the moment that
subdirectory is not included in the sources so no languages will be
enabled unless you add the actual translations before running
configure.

The .mo files are created in the locale/ subdirectory when compiling.
By default MPlayer will only look for them in the installed location,
so the newly compiled .mo files will not be found if you run MPlayer
without installing. You can set the MPLAYER_LOCALEDIR environment
variable to point to the locale/ directory to test the translations
without installing.