I have exact same problem as : https://c.mi.com/thread-2493987-1-0.html
I have mi band 3. It was out of power, so I plug it to charge but then instead of English appeared Chinese language.
I tried pairing the band but the app was resetting trying to download a new version.
After the new version was installed, I tied pairing but the phone did not find the band.
I saw the factory reset button and clicked on it.
Then, appeared instead of numbers, some Chinese letters/numbers which I could not read and consequently could not insert into the phone and could not reset !
Now, the phone can`t find the band, i tried using my old account and a newly created one but no success.
The band shows to pair it with a phone and some Chinese letters, info button and when i click it says: cmiit id 2018dp1565
The solution in thread was : You have to remember which account you really use in signing in on MI FIT app
But unfortunately, I don't recall and cannot find the account I used for sign in.
Surprise! I didn't expect Chinese on a Chinese smartwatch!