Many websites use the IP address being used to determine what language to display their content with, and to deliver advertisements that are "local" for the location of the IP address being used. Some websites like Google, Yahoo, and others allow the user to change language or locale preferences, that information is held in a Cookie for repeat visits to their domain.

Look for a method of changing the language for each web site and for saving that information. If you post those websites here, maybe someone will be able to tell how to set or change the language prefs for those websites.

Some sites automatically redirect you to a site in the local language, based on where your IP locates you.
There is usually a link on such websites choose a language or go to an international version that allows to chose the language.

If the Google (Firefox) or Yahoo home page is in the wrong language then see:

• Google: http://www.google.com/support/bin/answer.py?answer=873
• Yahoo!: http://help.yahoo.com/l/us/yahoo/homepage/homepage/basics/troubleshoot-02.html

You may need to clear the cookies from those websites and set an allow exception to preserve those cookies.

• Tools > Options > Privacy > Cookies: "Show Cookies" and "Exceptions"