How do you detect the user's language preference on ones computer?

Answer:

By using the Request object’s UserLanguages property you can return a list of the user’s language preferences. In that displayed UserLanguages, the first element of the array is the user’s current language on his/her computer.
Example:
In your web.config file, you need to set the following globalization tag with the values shown below:

<system.web>

   <globalization

          uiCulture="auto"

          culture="auto"

          enableClientBasedCulture="true" />

</system.web>

The above code is enough to have the user use his preferred language with his/her web application.