One of the requirements for requesting a new project within the Wikimedia Foundation is the localisation of the user interface. For a first project it was felt that we do not want to burden the new community too much and have allowed for the localisation of a subset of all the MediaWiki messages. When a subsequent project is requested for a language, we require a complete localisation of the user interface. This means all the MediaWiki messages and the messages of the extensions that are used in the Wikimedia Foundation.
It is important for the people of existing projects that the localisation is done centrally because this allows them to use their language in the user interface of Commons and other projects. Currently the localisation for many languages leaves something to be desired. This makes it harder for the people requesting new projects to fulfill this requirement.
BetaWiki has proven itself as a great facilitator for the MediaWiki localisation. It has a smooth web interface, it supports off line work by providing "gettext" or ".po file" import and export. I do urge people to support their language.
We are in the process of providing more stimuli to the localisation effort, I hope to inform you about this in the near future.