The defalt value for "/nextlabel" in <instruct> is "Next". I've change it into other language. And I've made:  /nextkey=" ".

 But I found that during the same experiment, sometimes it works and sometimes it appear as "Press [space] to continue".

It's not very important, our participants can understand that simple English. But it's interesting. I think it's because the program didn't have enough working memory to process the value of "/nextlabel", so it read the value of "/nextkey" and showed its own "/nextlabel".