Translation using gettext
From version 0.8.0, stellarium will fully support translation into other languages. The translation is performed using gettext. All the strings used in the program are translated and saved in special .po files. These .po file can be edited using a text editor or special program such as Kbabel. An easier way (but less efficient) is to use the Rosetta facility which allow to translate Stellarium online. If you speak a non-english language, please considere contributing to the developement of Stellarium!
Once your .po file is ready, you can compile it into a .mo file and test it in the real stellarium application to check that everything is correct. For example, if you are French and work on fr.po, save your compiled fr.mo file as stellarium.mo and copy it into the directory stellarium/data/fr/LC_MESSAGES/.
Re-run stellarium and there you are!
POedit po-file editor for Linux and Windows.
KBabel po-file editor for KDE environments