According to Telegram, “The Android app already supported multiple themes, so it had to go further with 4.7 by supporting multiple accounts. You can add up to three accounts with different phone numbers to your Telegram app, and then quickly switch between them from the side menu. Notifications will keep coming from all accounts, unless you change this in the Notification settings.”
As for quick replies, this will be similar to WhatsApp where users can now swipe left on any message to quickly reply to that message. That message will be quoted in your reply to give it a bit of context which might be useful if you’re referring to an older message or in a group chat. In addition to these new features, the latest version of Telegram will also include improvements for handling/downloading media, better link previews, albums in Secret Chats, and more.