If I add a spell check button to the Cute Editor toolbar will it use the British English dictionary if someone in England uses the spell checker? If they are entering Spanish and are in Spain will it use the Spanish dictionary? 

Hi,

Yes, by default, the editor will checks the browser language and siwthc the correct language for the user, also it will use the related  dictionary too.

If you have set the  CustomCulture for the editor, then it will use the culture what you set as the sepll check dictionary .

<CE:Editor ID="editor1" runat="server" CustomCulture="en-us">

Regards,

Ken