Is someone know if is exist a similar site to merb but in french?
There are a few similar sites around, but I don't know of one specifically in French. As you know already since you did it a few times, you can post both in French or English here. Many members are French and can help you out. French is also commonly accepted here even if it reduces your audience a little. The worst that can happen is that someone else will ask for a translation to English. This is more likely to happen if you post a review in French only, and even more so if it contains some "juicy" stuff