At first I thought this was just overreacting. Or that you were just upset without reason. But you did list reasonable alternatives that weren't followed.
Other, whisper, and group.
I don't mind it too much, but the language preferences should limit what language is spoken to some degree. There are no rules to prevent some friends and I from switching to Japanese or something and having an open conversation with each other there in English without worrying about being interrupted for the most part. It's excluding the people who speak that language. And if it were an exclusive conversation it should preferably be in private such as whispering or groups.
Edit.
I read through the Code of Conduct again and rule 1B states: You may not spam, flood, or repeatedly make duplicate posts. Messages composed of gibberish and messages outside of their designated chat channels are considered spam;
Therefor there is a rule for this.
And the code of conduct itself states:
PokeMMO's Services are governed by certain rules. These rules (the "Code of Conduct") are maintained and exclusively enforced by PokeMMO's Staff and must be adhered to by all users.
So you are in the right to bring this to the attention of PokeMMO staff so that they may enforce this.