Install asterisk-core-sounds-ru by entering the following commands in the terminal:
sudo apt update sudo apt install asterisk-core-sounds-ru
asterisk PBX sound files - Russian
Asterisk is an Open Source PBX and telephony toolkit. It is, in a sense, middleware between Internet and telephony channels on the bottom, and Internet and telephony applications at the top. . Asterisk includes a set of standard sound files in various formats. The core part of that collection in Russian, by Maxim Topal, is contained in various encodings in packages asterisk-core-sounds-ru-*; this package registers these through the alternatives system to provide the default "ru" and "ru_RU" (Russian) sounds.