Prerequisites:
1. Have a favorite Cyrillic font that can be used at least. I'm not sure about Android 4.x, but my Meizu MX3+Flyme 5(Android 5.0. 1) supports both otf and ttf files.
2. willing to root the phone.
-Specific operation: 1. Back up all the system files mentioned below, and then get root privileges of the system. Please search by yourself for specific methods; Note that obtaining root permission may bring some side effects, including but not limited to abnormal functions of the mobile phone (such as partial function failure, inability to turn on the mobile phone, unlimited restart, etc.). ), after-sales service loss (see the agreement of the mobile phone manufacturer for details), privacy and security risks (if the malicious software obtains root permission, it can read and write any information, such as reading the saved account password and installing other malicious software).
2. Prepare tools for modifying system files, such as a file manager, virtual terminal, or adb on PC (it is strongly recommended to prepare a tutorial for modifying system files through adb, and authorize adb debugging in superSU and mobile phone systems in advance. In this way, even if the phone can't be turned on, there is a chance to fix most problems, and in the worst case, there is a chance to back up the data in the phone.
3. Use the tools in step 2 to put Cyrillic characters into the /system/fonts folder, and modify the permissions of the new file (please refer to other files in the same folder for specific parameters of permissions, generally RW-R-R-, or 644).
4. Edit the font configuration files under /etc, which usually include fonts.xml, system_fonts.xml and fallback_fonts.xml, and may also be related to some configuration files under /vendor/etc. It is generally enough for the file names to have fonts. Android 4.x may involve fewer files. (You can also copy it first, edit it, then copy it back to overwrite the original file, and finally pay attention to modifying the permissions).