First of all, it's my fist post and I am very pleased by join this forum.
So, my point is:
A few years ago, when I got involved in fansubs, I used to make karaoke effects using Adobe After Effects.
Now I am trying to find a Linux alternative. So, is KDEnlive able to do it?
(Sorry for my bad english)

I can't think of any easy way to do this with Kdenlive. If you already have your file with lyrics and timing, the least painful method might be by using any karaoke software and simply capturing its output. PyKaraoke is the first thing I came across: