I have a snapshot (although don't attach it here because of its large size) that shows a text typed in Word (MS Office 2000) sequentially in German, French, Polish, Belarusian, Ukrainian and Russian (locale is KOI8-U and supports only English, Russian and Ukrainian letters).
I can say even more. Even if user have broken locale or/and broken input he can write non-English letters anyway. I think this is big improvement because there many users (at least in Russia) who have such troubles with Wine. For example user can have correct locale settings (LANG, LANGUAGE and LC_* all equals to ru_RU for example) and perfectly working locale-enabled programs like cal, nano or date but Wine sometimes cannot work correctly: it display Russian letters perfectly, notepad and others has Russian GUI but input of Russian letters doesn't work because of famous "err:keyboard:X11DRV_ToUnicodeEx Please report: no char for keysym" error (sometimes this is becaue user forgot to launch locale-gen but sometimes this is because of broken libc - in such case there is no simple solution, only recompiling). With this patch Wine works out-of-the-box anyway - that also means better integration with X. I found other small improvements as well (within source code). ...And of course + all major improvements listed by Oleh himself.
My opinion: this patch gives better integration with X+XKB environment and probably can be useful for many users. So I think it worth trying...