Hope it is ok to write in English here, as I still understand most of what you write (my French was limited to two years at school approx. 25 years ago) but feel unable to answer appropriately in your language (which is beautiful, btw, especially compared to German, which is my mother's tongue).
I am the guy from AVS with the 8 dead pixels (ATM). Rest assured that I did do a dead pixel test after having received the pj - it showed zero dead pixels, which was 3 months ago. Although being new to dlp I do have some ancient (but still mostly valid) and deep knowledge of AV-systems and techniques.
I registered here because while researching my problem I stumbled across sebdoc (from this forum) who had a similar problem (and managed to deal with Gearbest via PayPal) to contact him (thanks for your support!).
It might be some bad ti dlp chips (so not a Xiaomi Problem) but this will still affect a lot of people - and it does if you Google "dlp dead pixel".
In addition: rest assured that I did contact Xiaomi directly (to have something to argue with Gearbest) but they where VERY reluctant to either help or even provide information for a product that is not sold in their international online shop. So they have proven to be no help at all.