As a rule, all China / EN firmware versions are locked and the Global unlocked. Unless you buy an EU version of the device, there is the EU power supply included and the firmware is locked.
Locked Firmware = The firmware is locked and you can unlock it just by tying it up with a Mi account and unlock it again. This is usually needed to install custom roms or alternative firmware versions, for example. A locked firmware has no disadvantage and all services and apps work without problems.
Unlocked Firmware = The firmware is unlocked and you can easily install Custom Roms or alternate firmware versions. Since Xiaomi has changed the process, most China devices are unlocked with Global Firmware. The only downside right now is that this firmware can not be lured back and Google Pay is not working. Apps like Netflix, Pokemon or Banking Apps have no effect, they usually work.