Thanks clutchdust.
I got hold of a user guide on t'internet and it has a language option in the set up menu.
Also got info from previous owner that if you re-boot computer with CD out and then insert CD, it asks for language required at that stage.
I bought the unit recently to install into my 4.4HSE, which has the wiring in the load space for it, but it would appear that fitting the display unit and other associated bits and bobs was going to be a nightmare - so I sold it on.
It's the new owner who is having the problem.
Appreciate the help though.