Chinese on UK HTC8X

[DuncanF62]

I've moved to a Lumia 930 and given my HTC 8X to a friend. We are struggling to get Chinese on it. She previously had a Lumia 520 and on both that, and my Lumia 930, we can setup the phone for both English and Chinese. The phone is originally O2 but now unlocked.

The HTC allows me to download the Chinese language packs but I can't find a way to select it as the primary language. On the Lumia it is as simple as selecting Chinese when in Settings-> Languages.

Is this possible, or am I running into the same ROM issues that stopped Developer Preview users from getting Cortana by switching to US English?

Any help much appreciated.

Thanks,

Duncan