The language settings in your browser should include all of the languages that you can read, in order of preference. This lets your web browser negotiate the language you get with the web server sending you pages. If it isn't set right, you can miss out on stuff you could have read.
Mozilla, Netscape 6 and Netscape 4
From the "Edit" menu, select "Preferences...". In the "Navigator" section of the preferences, select the "Languages" section.
From there, you can add languages from the built-in list.
Mozilla Firefox
From the "Extras" menu (or "Edit" in Linux), select "Preferences...". In the "General" section of the preferences, select the "Languages" section.
From there, you can add languages from the built-in list.
Internet Explorer 5 and 6
From the "Tools" menu, select "Internet Options...". In the "General" tab, click the "Languages" button.
From there, you can add languages from the built-in list.
Other Browsers
See Debian's web site on setting languages for information on other web browsers.