ok, i got the first answer :

tazwok gen-list /home/slitaz/packages/

make my /home/slitaz/packages/ a repository, and as far i build packages with version higher than the one in the official repo tazpkg will install the right packages.
so to share with some other user should i make the files available through a webserver?

It does not work, somehow after tazpkg recharge tazpkg can only see local files and not the official repos one.

root@sl3:/home/fabio# cat /var/lib/tazpkg/mirror
/home/slitaz/packages/
http://mirror.slitaz.org/packages/3.0/
http://download.tuxfamily.org/slitaz/packages/
http://mirror.switch.ch/ftp/mirror/slitaz/packages/
ftp://mirror.switch.ch/mirror/slitaz/packages/
http://www.gtlib.gatech.edu/pub/slitaz/packages/
ftp://ftp.gtlib.gatech.edu/pub/slitaz/packages/
http://mirror.lupaworld.com/slitaz/packages/
http://slitaz.c3sl.ufpr.br/packages/
ftp://slitaz.c3sl.ufpr.br/slitaz/packages/
http://slitaz.mirror.garr.it/mirrors/slitaz/packages/
ftp://ftp.pina.si/slitaz/packages/
http://distro.ibiblio.org/pub/linux/distributions/slitaz/packages/
http://ftp.vim.org/ftp/os/Linux/distr/slitaz/packages/

any help?

Maybe the add-undigest/setup-undigest/list-undigest/remove-undigest feature of tazpkg is what you want.

http://hg.slitaz.org/tazpkg/raw-file/tip/doc/tazpkg.en.html

thanks a lot Mojo, you point me in the right direction, i can continue compiling my stuff and start reading more carefully documentation ;-)
i'm planning to migrate my home network from archlinux to slitaz but for some cohabiting reasons i need italian language :-)

the language aspect is something that really should be solved - perhaps a separate repository for every language could be the solution, but I don't think that's efficient - I think on the mailing list, there was discussion , somebody is going to work on translation - perhaps this is a possibility to discuss this in the forum

i could help in italian translations, if there is no hurry.
could be a solution to build every package against a language and make tazpkg install the localized version of a package depending on the value of the locale in /etc/locale.conf?
so the default could be glibc-base and the localized versions glibc-base-it glibc-base-fr and so on? sure the build server would have lot of work, maybe this could be done only for the stable release and not for cooking.