If you read the thread earlier you posted on, or talk to 'scoubix' (Nicolas), you will see that you will need a navigation computer unit in the boot that has the language you require "built in" as one of the 3 languages. Very difficult to add a different one.
If you have the Hi-Line TV screen navigation system, I have a BMW Mini Mk.4 DVD SatNav computer/drive unit in Italian/French/German unit for sale, including V.32 SW (Euro 90 + postage), which should be a "plug and play" replacement for the CD-based MGR unit I assume you have in your boot. All you would need would be a BMW maps DVD.
Maybe it would work with the low-line navigation (the one without the TV screen), but I am not 100% sure of that.
Send me a PM (personal message) please?
David