Will I be able to change the language to English and continue to use the phone without any chinese interaction or should I use a custom mod?
The base MIUI is quite closed source and opaque (there was some brouhaha on XDA about it) I'm sure. There are several spin-offs and/or AOSP merges in different languages on XDA.
These are specific links to current MIUI ROMs (current as at 29 Aug 2011)
However, I'd suggest you monitor the relevant device forum at XDA and see what's out there. Versions change, ROMs come and go, threads are closed/new ones opened etc so the two links above may not be reliable over time
I have a HTC Desire: there were half a dozen MIUI ROMs for this a few months ago. YMMV of course
Note also that ROM developers are leaving XDA because of the noise and stupid users. Hence the galtnet MIUI link (which I got from XDA). So you may find less info than you expect on XDA
You said MIUI but I can recommend Oxygen for the SGS2 (I use this on my Desire)