Do not deal with people who ask to contact Telegram scam there are many in Telegram contact using PM and use escrow service.
What programming languages that dev must have?
Blockchain is not a programming language it is a way to manage data. You can deal with it in several programming languages.
I asked him to contact me on Telegram, because I wasn't able to PM him. I didn't really understand why do you say if someone ask for a contact on Telegram, it's an instant scam.