@Ambraven I do agree. However, I don't think it is useless though. I mean, it's fun to learn, fun to create. And learning something like Esperanto is easy enough so that with only little knowledge, it is able to understand and talk about basic things.
However, I think there are also other issues (about Esperanto, but it may be applied to other languages as well) : Esperanto aims to be an international language, but is based only on european ones ; it is really binary (probably less inclusive than french, I really don't like marking the gender of every word).