It appears that autogen.sh doesn't like es.po if it isn't mentioned in

[tinc] / .cvsignore

Makefile Makefile.in aclocal.m4 config.cache config.log config.status configure
config.guess config.sub install-sh missing mkinstalldirs ChangeLog
config.h.in stamp-h.in config.h libtool stamp-h build-stamp
intl