To make use of .NET resource globalization simply edit strings.resx and save as a new file with the following naming scheme:

strings.<CULTURE>.resx

Some sample values for <CULTURE> are:

en      English
en-AU   English - Australia
en-GB   English - United Kingdom
en-US   English - US
de      German
es      Spanish
fr      French
fr-FR   French - France
fr-CH   French - Switzerland
ja      Japanese
zh-CH   Chinese - China
zh-CHS  Chinese - Simplified

See the reference on the System.Globalization.CultureInfo class for a list of possible culture languages.

Example of specifying the UI Culture on a web form:
<%@ Page UICulture="de" Culture="en-US"%>

Example of specifying the default UI Culture in the Web.config
<configuration>
   <system.web>
      <globalization
           culture="en-US"
           uiCulture="de-DE"
        />
   </system.web>
</configuration>

Example of changing the UI Culture at runtime:
Thread.CurrentThread.CurrentUICulture = new CultureInfo(Request.UserLanguages[0]);