I think it's possible construct to construct a (very weak) argument for the random user agent rotation, but why split the spring if not to avoid being flagged.
On the other hand, I find it hard to believe that Telegram would risk a Play Store ToS violation, given how many tens of millions of users use the app.
Pretty sure at the point you have over a billion(!) installs, even Google affords some leniency towards its Play Store policies. Or at least we are about to find out anyway..
Meanwhile, indie developers with smaller user base are subject to unappealable automated decisions.
I'm not sure if Google will start flagging the IP addresses of the users because of each request having a different agent. That would render normal Translate unworkable for them too!
Isn't Google going to move to always having the user agent be the same anyhow? They've already decided to break that contract with the tech community, so I don't see that they have much room to talk there.
That contract was torn up a long time ago. Or do you really browse the web with "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/96.0.4664.110 Safari/537.36"?
On the other hand, I find it hard to believe that Telegram would risk a Play Store ToS violation, given how many tens of millions of users use the app.