In Web.config or ideally in user.config:

<add key="UseCultureOverride" value="true" />

You would set this to true, then you would need to add a setting for each of your sites like:

<add key="site1culture" value="it-IT" />
<add key="site1uiculture" value="it-IT" />

<add key="site2culture" value="nl-NL" />
<add key="site2uiculture" value="nl-NL" />

The numeric part of the key corresponds to the SiteID so tha it is possoble to configure different sites in a multi site installation to use different languages/cultures.

Note that culture determines which culture is used for string formatting of dates and currency, etc, whereas uiculture is what determines which resources file is used for string localization. For string localization it will fall back to English if there are missing keys in the translated resource file(s).

If you are not forcing a specific language then the default behavior is to adapt to the prefferred language according to the user's browser language settings.

Created 2011-08-02 by Joe Audette