Like MediaWiki itself, the mapping extensions are supported for their localisation by the translatewiki.net community. Translatewiki.net provides you with both a web interface for localisation as well as the possibility to export gettext (or .po files).
Every day, localisations are exported from translatewiki.net to the Wikimedia Foundation's SVN repository. In this way the latest information is available for you for download.
If you would like to help translate the mapping extensions (and other MediaWiki code), there is a simple process for doing so: just register on translatewiki.net, then make a request on this page.