他们在做纸飞机英语可以翻译成"They're making paper airplanes"。这个短语的来源可能是有关制作纸飞机的活动。例如：
"They're making paper airplanes in their free time."（他们在业余时间做纸飞机。）
"The kids are making paper airplanes to pass the time on the long car ride."（孩子们在漫长的车程中做纸飞机打发时间。）
"She's an expert at making paper airplanes - she can make them fly really far."（她是做纸飞机的专家，她能做出飞得很远的纸飞机。）