Coming back to this thread after one year.
One simple approximated implementation for truncated_normal to 2*std.
def truncated_normal_(tensor, mean=0, std=1):
    size = tensor.shape
    tmp = tensor.new_empty(size + (4,)).normal_()
    valid = (tmp < 2) & (tmp > -2)
    ind = valid.max(-1, keepdim=True)[1]
    tensor.data.copy_(tmp.gather(-1, ind).squeeze(-1))
    tensor.data.mul_(std).add_(mean)