My implementation of RSA does not work with Cyrillic. How to fix?

Question

Java

For the tutorial project, you need to implement a client-server system with message encryption. The client, using the public key received from the server, encrypts the message and transmits it. The server decrypts it. With Latin, everything works as it should, but if I send a message in Cyrillic, then it is decoded incorrectly. I am using BufferedReader/BufferedWriter for socket work. When creating their objects, I specified the utf-8 encoding, it did not help.
https://github.com/Nikitae57/os_rsa