Ok, as nobody answers, I list what I've been trying :
After having rooted my A500 and installed Acer Recovery, I tried to install the USA OTA rom from Acer recovery but it did not work (I get the exclamation mark + green bee screen when I reboot).
I installed the morelocale2 app which is supposed to fix some localisation problems (language, etc). It kinds of works, but does not fix my android market issue.
I found some OTA update stock ROM (can't post the link, google : "Acer Iconia A500 Original and OTA Update Stock ROM Package List") but I don't know which one corresponds to my A500 (my build number is : xxx1.135.02xxx).
I don't know what to do now ?
CAN ANYBODY HELP ME ????