Well I see what you did there. Indeed it isn’t. (privacy)
So about “Private” I am aware that it’s not the best example: Street (“private”) vs a massive crowd (server). However my idea was to address the typical friendly wink to another person - because I assumed that most if not everyone is familiar with it (saying Hello to someone in the street, based on how you are used to saying it to that person, i.e. “Wassup”). To paint it more closer to the situation: If you think of a really huddled city, for example you can watch this in Asian Metropolitans. Then it gets rather close to the server one: Someone talks and many are “hearing” it.
To remind: The topic in my previous comment was, that some are just doing that without a purpose to only speak “their” language(s)! But naturally, only a “hi” basically. Instead they might even speak English usually. And this is where the example hits: Similar to on the street, you just say naturally: “Wassup” to a mate. Then the analogy is: Someone else commenting it on the street: “Hey speak in the language we can understand too. It’s polite!” 
And again this is only a part of people’s behaviour. There are, of course, sometimes rather strong and sometimes light approaches. (talk in “their” language only (no exceptions), or answer via ‘/whisper’ only, respectively.)
I think at least when you see the chat is full, you should consider the whisper.
By the way, for this reason: In the Asian Metropolitans that I know, it is frowned upon to talk in a public train for instance - Similar to your explanation on a server: Basically some people frowning about stuff they are not interested in (another lang. for instance, or a certain topic, or just too much noise! - It’s uncomfortable to them). Then let me tell you: In other countries in Europe this is the most normal actually, where there are more than 10x languages spoken in full train, some times. (I.e. Belgium, Germany, Montenegro, Serbia) People are used to this. But certain people just don’t know about it, or are not aware of it (more or less).
The main problem is people think they know everything. (“Dunning Kruger Effect”)
(I don’t know everything, neither. But I know some, from often travelling, which the point was about: To add perspective)