I have bought an Omnia and it is in SWEDISH. There is a manual in Samsung Omnia which guides you to change the language in English.
Instructions are as follows:
If you have the microSDTM memory card supplied with your device, go to step 1. If you do not have the microSD memory card supplied with your device, go to step 6.
1. Press and hold to turn your device off (if necessary).
2. Insert the supplied memory card.
3. Press and hold to turn your device on. The multi-language installation program runs automatically.
4. Tap Install.
5. Wait until the installtaion files are copied to the device.
6. From the Today screen, tap Start → Settings → System tab and select .
7. Tap an MLI file and Select.
8. Read the instructions and tap Change language.
9. Enter 1234 and tap Yes. The device restarts automatically.
10. When the language selection window appears, scroll to a language by pressing
11. Press to select the language.
12. Press to select the Yes check box.
13. Press to tap Next.
The firmware is installed and the device restarts automatically.
The problem is after step 9, nothing happens. I called Samsung support and they send me an updates .MLI file, but it didn't work for me as well.