Not playing down the importance of flight and crew having to be able to speak English but I was alwys taught in CRM sessions that no matter how good your english is, when it's not somebodies mother tongue that when encountering a stressfull situation the brain will always revert to the speakers mother tongue to be able to focus more on the actual problem. Maybe the captains english was good enough in normal day to day situations, this incident made it probably a lot harder for im to understand and reply to simple instructions