Which language useful for telegram bot?

Answer 1

I'd go with Python

Answer 2

The Telegram API uses REST over https protocol. It means the commands are simply web addresses (with specific parameters). You can use literally any programming language, whatever you are comfortable with. You can even find many samples for Python, JavaScript, PHP, Rust, Kotlin, Java, Go, and many more.

https://core.telegram.org/bots

https://core.telegram.org/bots/samples