I understand your concern about the WTF emotion but, despite what that article says about the MPAA and their standards (I've always thought they've been kind of off about their rating standards...), your argument doesn't make sense. W.T.F. is an acronym that is ambiguous if the person doesn't already know what it means, and, if they do know what it means, I think we can safely assume they won't be demoralized by another player using it offhandedly while in game. There are much worse things someone could do other than that, which I don't care to mention...
However, if anything I think it could be questioned into removal because it's English. Teeworlds is an international game and I think it's kind of only fair to use emotions without a specific language attached to it, or at least, ideally.
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The type of values you're trying to keep are kept by far and few in between in this world, but I commend you for it, since I consider myself a Christian too. However, to be honest, those values are fairly unrealistic. I can understand wanting to protect children but they and their parents will have to come to the reality that this world is a messy place, filled with those we rather not be around. It's unfortunate but true. If something like the WTF emotion can demoralized their childhood innocence then their parents have done them a disservice to them by making them so morally week... It's just life man, unless they plan on being Amish. :\
And on the whole chat filter thing, it has been discussed before here under "Community features", and it will not be implemented for two main reasons. One, most people don't care that much; players are able to mute other player if they want to if their language is bothering them. And two, those chat filters are easy to get around and are therefore, pretty pointless. I've seen chat filters implemented before and if someone really wanted to give someone else a piece of their mind, they were going to do it... and do it creatively.
Give others the respect you wish to be respected with. In the mean time, enjoy the website!