What i must learn for be an Ubuntu Mantainer?

[Alessio]

Skills? Languages? Any other?

[az]

There are ubuntu specific things, you can find that on the Ubuntulinux suite.

As for skills and languages, look at the Debian new maintainers guide.
http://www.debian.org/doc/maint-guide/

also:
http://www.debian.org/devel/join/newmaint