Two days ago I wrote how to upload English for Xiaomi Mi Band 3. Uploading the Polish language looks exactly the same, you only need to upload a different version of the Mi Fit application. Here, I will describe in brief the whole course of the installation, if something is not clear to you, return to the entry two days ago.
Xiaomi Mi Band 3 installation of the Polish language
You need an Android phone. Remove the Mi Fit app from the Google Play store and install from the link below
Launch the newly installed application, log in to your Xiaomi account and pair with the Mi Band 3 wristband. The headband will automatically update to the new version of the software and will start again with the interface in Polish.
The interface is almost entirely in Polish, the only lack is the description of the weather under the temperature. It is in the form of question marks, but it will be better soon. Now you should "finish" the installation of the Polish version, disconnect the Mi Band 3 band from the Mi Fit application and remove the application from the phone. You have to go back to the version from the Google Play store, download the official Mi Fit app and re-pair your armband. The whole interface will be in Polish, and bushes that describe the weather will be replaced with English equivalents.
Important information for iPhone users. If you carry out the aforementioned substitution of the software and then re-pair the iPhone with the wristband Polish language will be! Only the weather description will be in the form of question marks, but everything can be seen from the graphics, also nothing terrible.
3 July 2018 update
The .apk file has been swapped, now the weather is in Polish, but only when the Mi Fit version is installed from the link I provided. Of course, people who depends on the weather in Polish can stay with the modified version application. When we install the official from the Play Store, the weather description returns to bushes or English. For bushes if the language in the phone is set to Polish, when the language in the phone is set to English, the weather description will be in English. Besides the detail with the weather everything is in Polish.