Download original MIUI 9 v126.96.36.199.NDBCNEI China Stable either Fastboot or Recovery ROM from direct hot link for Xiaomi Mi 5X codename Tiffany. This ROM package may come in handy especially if you have either Type 2 or Type 3 device of Mi 5x. Most of Tiffany devices shipped worldwide run unofficial (read: modded/hacked) build of MIUI 8.5. Therefore, it is safer to flash back your phone onto official MIUI build. Despite the one available now is still China Stable, since the device is not available globally yet, you can enjoy a more secured experience in using an Android phone. Of course the Chinese variant does not have Google Apps (Gapps) like Play Store or Gmail by default, but you can manually and easily install it by yourself.
Alternatively, if you want to have your own local language instead of Chinese or English, the one from Xiaomi.EU ROM will be the best and most viable ROM to have.
MIUI 9 Fastboot ROM:
MIUI 9 Recovery ROM:
How to install? Follow this guide to easily flash MIUI 9 via Recovery method.