If your favourite language is interlingua, that is. Or if you are willing to record your voice and submit it for inclusion, chances are that the next version of mappero will support your language, with your voice too! :-)
Just follow the detailed instructions in this thread, and have the community enjoy your voice. :-) All languages supported by the N900 are supported by Mappero voice navigation too.
Mappero 3.0+beta7 is now in extras-testing, and with the advent of the PR1.2 release it shouldn't make the device unstable anymore. Please install it, test it, and report your feedback and hopefully it will get promoted to Maemo extras soon.