thanks for your answer Tuxor. The dictionaries were downloaded from the site mentioned in 'Updates Post' of Booxtor:
http://abloz.com/huzheng/stardict-dic/. I repeat that they are just recognized, but seems to not work properly when i try to find words. If i select a random dictionary from installed ones and try to find a word, the dictionary app brutally turn down, returning to main menù.