Filters are useless. You can beat them with l33tsp34k or british pronounciations (ye know, unneccesary vowel and consonant substitutions.. fug the fug'n fediddleers!)

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Best filters are humans. HTC tried putting some moderators, but they arent on all 3 countries at once or in all sectors (purple text) at once and cant really be effective.
So the best option is a VOTE system. It works wonders in many other online games.. NETREK (oldie game) comes to mind...
person A is being a real jerk in team chat.. if you can get X # of votes then that person was EJECTED from the game for an hour.
To prevent abuse, certain limits would be placed.
Like, total players in arena when vote is started: X . % of votes needed to eject: X / 3 (3 countries) when vote is cast in CH1
CH2 vote = 20% of the X # of players in country when vote is started in CH2.
Penalty can be less severe though.. perhaps a 10 minute muting?
And since this is kept on the server, logging off and back on does not remove the mute or eject penalty.