Like what was done on gtk/language-names.c, acquire the language names via the
native Windows NLS APIs, eliminating a run-time dependency on iso-codes on
Windows.
Remove g_auto*() usage from these sources and use the traditional
g_free(), as g_auto*() are GCCisms (or CLangisms).
Also, don't include unistd.h unconditionally and stop including
langinfo.h and dirent.h, since they seem to be unused.
https://bugzilla.gnome.org/show_bug.cgi?id=773299
