if you are a maintainer of yum and you need to update the translations you should do this:

 - tx init
 - tx set --execute --auto-local -r yum.3-2-x-po-yum-pot 'po/<lang>.po' --source-lang=en --source-file=po/yum.pot

to pull the latest of everything:
 - tx pull -a -f

to push up new changes to the .pot file

 - tx push -s -t

More info here:
http://lists.fedoraproject.org/pipermail/trans/2011-January/008573.html

Note that username/password settings are stored in ~/.transifexrc