Now Mi Fit 4.09 with Firmware 10.0.6.16 does support Thai but I have to change system language into Thai First. I don't want to change my system language into Thai so I used app "Mi Band Master" from Play Store to change my mi band language into Thai then uninstalled it. Now Thai Languange is...
I'm in Thailand with Global Version. now latest version is 10.0.6.16.
I downloaded "Notify & Fitness for Mi Band" then use this app to update Firmware (any) and go back to Official Mi Fit then It updated mine to the latest official version.
I hope this method it will also work for you. good luck.