I have a thing I’m writing that will go into more detail, but in short Telegram’s client applications (which are licensed under various incarnations of the GPL) are updated frequently while the source code in their publicly available repositories lags far behind. In addition, they use a number of open source libraries that at the very least require attribution, but Telegram does not follow their terms.
> while the source code in their publicly available repositories lags far behind
I don't think this violates GPL. GPL requires you to be able to receive the source if you want to, not that it be on an online repository. You might have to request it and have it sent to you.
I mean, I could, but I think it's fair for me to assume that the GitHub repository that the official website links to as the source code for their client is where they’d publish up-to-date code.
They might well publish it right there if you ask. Just saying they haven't violated the license as long as they have a written offer to provide you with the source code somehow if you ask. (That's what GPLv2 seems to require.)
They provide no alternative "written offer". On the website, they directly point to GitHub for the source code offer: https://telegram.org/apps#source-code
