There is a question here but that is for Ubuntu on PC.
I have the same question for an android device.
Is there a way to have two copies of telegram app in Android each with a different account?
I'm using the version Kitkat 4.4.
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Use the Parallel Space app. Using this app, you can run more than one copy of almost any app. Here is a link to the app: https://play.google.com/store/apps/details?id=com.lbe.parallel.intl
TL;DR: It's available officially.
From version 4.7 of Telegram (December 30, 2017) it's available officially in the Android app.
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.