I've changed my MiPhoneManager (v1.0.4.5271) to English by copying the translations from the translated DLL on the MIUI forums over to the new DLL.
You can grab it here.
Go to your install path and replace "Chinese.dll" with the one you downloaded. The install path is usually "C:\Program Files (x86)\Xiaomi\MiPhoneManager"
Before:
After:
