First of all, thank you for helping translating SàT :)

NOTE: *.po files are in i18n directory

To translate a file, you can use a dedicated tool as the excellent gtranslator:
- use the template .po file (e.g. sat.po) and name it to your translated language (e.g. fr.po for french); you can preferably generate a new template directly from the source with the following command (eventually adapted):
> xgettext -L python -d sat sat.tac tools/*py plugins/*py

- use the choosed tool (a simple text editor can be sufficient) to edit the file: e.g. gtranslator fr.po

- once you translation is finished (or partly finished: the english sentences are used if there is no translation), you can test them by generating a binary and moving it to the right place with the following commands:
> msgfmt -o sat.mo fr
> mv sat.mo i18n/fr/LC_MESSAGES/sat.mo

/!\ Note that you don't need to precise the file extention mith the msgfmt command, here fr mean "use fr.po file"

- if you have already a translation, and want to update it (new translations to do, some sentences have changed), you can use the following commands:
> msgmerge fr.po sat.po > fr2.po
and if everything is allright
> mv fr2.po fr.po

Don't forget that you can use the version-control system (mercurial, the "hg" command) to keep history of you translations.

You can check the fr.po file to see how it's done and to know what to put while you set up you translation tool.

Trank you again for you help, don't forget to give me your name and contact mail so I can credit you, and don't hesitate to contact me if you need help (goffi@goffi.org).