Mi4 Play Store Problems. Buggy Update?

Feb 17, 2015
Hi,i've had my mi4 for about 1 month and everything has been fine until one day i woke up and my phone was in chinese and i couldn't access my play store and it had deleted my clean master everything was really weird. So i deleted my play store and decided to add it back manually buy downloading the apk but still no luck. When i pressed the play store it would close after 0.5 sec. I brought it back to the shop i bought it from and they helped me downgrade it. So now my mi4 interface has been changed to a mi3 interface, my current version is MUIU KXDMIBH34.0 and there is another available update MUIU V6.3.9.0 is it safe to download and will it take me back to my old interface?