In Betawiki, a lot of localisation is done. Much of the work starts with importing the localisation from a Wikipedia. The existing work is expanded upon but also the existing work is improved upon. An obvious example is the inclusion of plural support. When a lot of such work is done, it has been committed and it has gone life on all the Wikimedia Foundation servers .. you want to see it best on your own project.
This will disappoint, and it will disappoint for the best of reasons. There are two types of localisation; there is the language localisation, this is what we do at BetaWiki, and there is the project localisation. In the project localisation there are changes that are specific to the project. You do not want to overwrite these. What a moderator may want to do is delete all the local language localisations. In this way only the project localisations are left. In this way all subsequent improvements to these language localisations will become available when they do.