Switch Menu and Dialog language in Control Panel->Regional and Language Options->Drop Down NOT possible?

On certain WinXP system I can go to Control Panel->Regional and Language Options->Languages Tab
and find at the bottom a drop down menu for selecting the language.

Much to my surprise this Drop-Down menu does NOT exist on certain other WinXP installations.
It is not greyed out or disabled. No it does NOT exist!

Why?

Do I have to install additional language packs in advance?
Is this possible at a later time or do I have to do this during initial WinXP installation?

Or is this a matter of the bought WinXP version?

Camille