Programs to use for translation
Recommended PO file editors are (in no particular order):
- XEmacs (with po-mode): runs on Unices with X
- GNU Emacs (with po-mode): runs on Unices
- KBabel: runs on KDE
- KAider: An alternative (replacement?) of Kbabel for KDE4.
- poEdit: Linux, MacOSX, and Windows
poEdit does support multiple plural forms since version 1.3.. - OmegaT is another translation tool that can translate PO files. It is written in Java so it is available for multiple platforms (including GNU/Linux and Windows). It can be downloaded from SourceForge.
- For Mac OS X there is AquaEmacs and a port of GNU Emacs available using carbon for OS X. Also see the Emacs wiki for more usage help and tips. po-mode is not included, but is easy to add. Get it from the GNU gettext distribution.
- GNU Gettext (Linux/Unix) used for the GNU Translation Project. Gettext also provides msgmerge that makes merging translations easy.
- Vim (Linux/Unix and Windows versions available) with PO ftplugin for easier editing of GNU gettext PO files.
- LocFactory Editor (OS X).
- gted is an eclipse plugin that turns eclipse into a gettext editor. Eclipse is written in Java, so this editor is platform independant.
Be sure to get a recent version for all editors, multiple plural forms are a recent addition to the gettext standard.

gtranslator has been around
gtranslator has been around and works fine under GNU/Linux:
http://gtranslator.sourceforge.net