Surprisingly, using offensive language is something that isn't permitted in Travian. It seems however that multihunters (MH) have no way of know if someone is using an expletive in a sentence. The only way to get their attention is if you use foul language and are reported to the MH by another player. This is probably the coolest way of getting revenge on a player because you're protected from them for a few days (during the ban) and they are deprived of playing Travian.

There is another form of offensive language that will get you in trouble with the Travian moderators on a server. If you try to coerce another player into taking a particular action out of fear of "what you might do" you are violating the game rules.

For example, let's say you have a player who's been sending you 1 hour's worth of resources every day. This is perfectly legal and within the rules of the game. You tell him that he can send his troops to your village if he doesn't want them to get killed. This in itself is also ok. However, if you tell your farm that in addition to sending you resources he has to send all his troops to your villages to protect you, thus opening his account to attacks from other players you are eliciting a particular action out of fear. This isn't only against the rules, it's downright unethical.

Offensive language doesn't have to be in the form of a swear word. It can involve manipulation and fear-instilled in someone to make them your slave.