5."fly-in":I may translate it to "远道而来"
Chinese firms tended to learn more from multinationals that had taken the trouble to build their own large sales forces in China, he says.
中国企业通常从跨国公司学到的东西更多,而跨国公司则在建立他们自己的巨大销售力量时困难重重
*** take the trouble是费心血的意思(make the effort)
forces means "any body of persons combined for joint action" here.
有些跨国公司努力在华建立他们自己的庞大销售队伍。中国企业往往能从这样的公司学到更多的东西。