Localise between different versions of English

FROM : Alexander Hartner
DATE : Tue Mar 04 23:43:48 2008

I have an application which I would like to localise, however i need 
to support two flavours of English, one for the British edition and 
another for the US. In particular the word "Synchronize / Synchronise) 
is cause me headaches. Interface builder only seems to give me English.

Any ideas on how I can achieve this.

Regards
Alex