I recommend reaching out to this student through using a knowledge of Bulgarian culture. Find something that Grigor likes and reach out to him using it. In the silent stage of development, children need to express themselves, and this can only be accomplished if you can find a way to break through the culture barrier. Encourage him to express himself in any way that he finds enjoyable. Art, music, and writing all help, but also be sure to build trust between the two of you by encouraging him in any way that you can.