Description
AFAIK tdlib is currently under "GPLv3 or later". I'd suggest to switch to a slightly more permissive license: "GPLv2 or later".
In my opinion, both GPLv2 and GPLv3 are sufficient to protect the essential software freedoms. I am fine with software I contributed to being used under either license.
However, IMO, the free software community also benefits from being able to reuse each other's code. So in some sense, free software benefits from less restrictive licenses (e.g. any free software project, not matter which license it uses could use software under a MIT-style license).
Some people have strong opinions on GPLv2 vs GPLv3, making them choose "GPLv2" or GPLv3" (without any "or later"). Sometimes copyright holders do not trust the FSF with future licenses, so they choose a license without "or later" (and when the FSF releases a new version, even one they might agree with, the copyrightholders might be dead, so the project can't change the license easily).
This results in some free software projects being GPLv2 only or GPLv3 only, while others are GPLv3 or later or GPLv2 or later.
Using a "GPLv2 or later"-license would allow more free software projects to use tdlib.
In fact, most (44) files in tdlib/src are under "GPLV2 or later"; there is only a small number (15) under "GPLv3 or later". The situation is similar for examples and tests, but there I'd consider the license question less important.
Philipp