MIUI ROM English Version for Samsung Galaxy S MIUI ROM is available in Chinese for Samsung Galaxy S. (There is an english site as well, but it doesn't list Galaxy S) After the install, according to the docs, I get this on the screen:

(source: miui.com)
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)


I9000: http://forum.xda-developers.com/showthread.php?t=1118682
SGS2: http://www.galnetmiui.co.uk


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

Edit: 

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)