This is not an original suggestion, just stealing it from some other game.
What I am suggesting is that you give us a custom filter that filters out and blocks some message. Now what I meant with “custom” filter is that we can add our own keywords that we think a potential spam message will contain (example: “g0ld” “WWW” “$15”).
The reason to have a custom filter is because everyone will have their own set of avoidable keywords which they can edit at their will, this will avoid the spammers from knowing what words they should not use in their message in order to “spam effectively”.
Oh, and to an extend, it can be used to fulfil the other suggestion I made in the forum (https://forum-en.gw2archive.eu/forum/game/suggestions/Block-any-message-that-is-not-English-1/first#post3177024)