Notice: the information in this post is not supported by Microsoft. The use of the method described below will revoke your support status for your environment. Use at your own risk
This question came up today and I remembered being able to change this for MOSS by changing the content database so I wondered if it would still work in SP2010.
Well, actually it does ….
The article I used as a source for MOSS can be found at http://sharepointlearn.blogspot.com/2008/12/changing-language-of-existing.html
the only change to the original article is that the Table name has changed in SP2010. Here is the updated information:
The language of the site is stored at SP Web level. It is stored in database in the AllWebs table. So you need to change the language in database whatever language you want. To change the language in database you need to fire following Query:
For changing the language of all sites in to ‘Dutch’ language:
UPDATE dbo.AllWebs SET Language = 1043
Changing the language of one site collection: (Dutch language)
UPDATE dbo.AllWebs SET Language = 1043 WHERE SiteId = [[SiteCollectionId]]
Changing the language of a single web or subsite: (Dutch language)
UPDATE dbo.AllWebs SET Language = 1043 WHERE Id = [[WebId]]
Before applying the new language, you need to verify that the language pack for the language that you want to apply is installed on your machine or not.