The language codes to use in your limewire.props file are the ISO language codes, as displayed on the
http://www.limewire.org/translate.html
Limewire is smart enough so that it will use by default (in absence of a LANGUAGE= setting in limewire.props) the same language as the default language detected by Java from your current OS environment (the language bar if launched from Windows XP explorer, the current system locale on Unix/Linux or the prebuilt OS localization on Windows 9x/ME).
So English is not necessarily the default setting, and if you delete limewire.props in your home directory, the next launch of Limewire will first ask you a language to use (you may ignore this step if you wish) and the minimum shared folders and connection bandwidth.
If you remove manually the LANGUAGE= setting from LimeWire.props, Limewire will run successfully in your OS default language.
Newer versions of LimeWire now allow selecting the language directly from the Display menu. This feature needs a restart to enable the new setting throughout the GUI interface, because the first attempt to use new language settings dynamically was abandonned as it required too much change to broadcast this event to many already initialized GUI components that cache internally many localized strings for performance reasons, and rebuilding the GUI completely was really too complicated.