Translation using gettext
From Stellarium Wiki
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 Rosetta facility which allow to translate Stellarium online. If you speak a non-english language, please considere contributing to the developement of Stellarium!