Chat text comes ???

Hello @Nikolaso, welcome to the forums. This is most likely due to the mods on the server or due to one of the mods you are using. If everyone else chat is fine, then it's most like just an isolated issue with you and the mods you have active. Also check whether it happens on other kinds of servers too (not just that one server), if it happens on servers hosted by other players or on a dedicated server with server mods, etc. Does it also happen on Klei Public servers? Does it also happen when you host a server and other players join you. You should rule out and isolate where the issue could be coming from.

My best guess it that it's a language mod that you don't have that others do on that specific server.

Did that other person all see the "??? ???" in chat or was it readable for them?

Sadly, bug reports on DST only covers issues with the base game (modless/no mods), so this may be suited to be reported to the specific mod creator that made the mod that is causing the issue.

If it's actually due to one of the mods you've subscribed to and have active, then you'll have to manually disable and enable each of your mods to figure out which one is causing this issue for you,. Then let the mod creator of that mod know about it.

That's all the advice I can give, good luck. 

As Zillvr said, it is probably due to localization mods that the other players are using. Some of the older localization mods were written before we had a proper system in place so anyone without the mod will not be able to read it.

To check if this is the case, please disable all client mods and then join one of the Klei official servers and see if you can read people's text.
If you still can't then please close DST and then run the Verify Integrity Of Game Files via steam.