the language is always in the chip, no matter if the chip like in grey back version is located in the wire loom to the cluster, or inside the back of the cluster like in the white or blue back.
Language shown as default is the one based on the country version. So if the car was ordered let's say for the U.K., the chip default language is U.K. English.
To change the language is shown on Johan's site here
BMW E32 - Tips & Tricks
Changing the OBC language:
The OBC language of the car will sometimes reset itself to German. To change it to whatever you like try this:
1. Turn the ignition to position 1.
2. Hold the CC button down for 10 seconds. Then the next language will appear.
3. Repeat this procedure untill you have the desired language.
The available languages are: Engish UK, English US, French, German, Italian, Spanish
http://bmwe32.masscom.net/johan/tips.../cc_button.jpg
If for example he disconnects the battery for some reason, the language might "jump" back to the default language, because it keeps the set stuff only as long as the internal "batteries" =
capacitors have "juice". And here we come to the next problem. The old grey clusters like in your friend's car and also my 11/88 750 have now very weak capacitors, best is to replace them against new ones.
broken capacitors in the instrument cluster can be the cause of the instrument cluster acting like its haunted
BMW E32 - Dash capacitor replacement
or
he can change to another cluster, blue or white one. Both fit in the car as long as they have the same fuel tank size indication etc.
But then he will have all the data of the donor car chip.
Like miles, VIN etc.
The chip in the brown wire loom to the cluster for the grey cluster version remains there (without function, you just need the wire loom with the plug), but if a white or blue cluster is installed, the chips/EPROMs in the backside of these take over the "reign".
If for example he would have had originally a white cluster, he could have bought another white cluster and just change the EPROM between these 2 white back clusters. It is NOT possible to change EPROM inserts between blue and white backplare clusters, they are of different size.