hi, maybe the sentence is trying to suggest to maintain a low / soft voice when speaking english. I don't know how can this possibly be, but to relate it to my grand mother's story about the colonization of Spain to our country, Filipino's then are not allowed to speak any other language but only Spanish. Therefore, should one wishes to speak "tagalog", they literally whisper it (otherwise the Spaniards will go after them.) :)

对，这个就是不要说英语的意思。。。这个是用在美国的汉语课堂上的，意思就是告诉学员不要说英语，要用汉语交流。。。就跟我们上英语口语课一样的，老师会告诉我们，dont speak chinese, if you got question, ask the teacher... whisper就是如果你要说就小声靠在耳边说、、、

Yes, whisper it so you can't be discovered...? Perhaps it means it's not appropriate to speak English in that situation (such as learning a different language at advanced level). I'd take it in a playful sense: it's OK to speak English, but don't make it obvious. :) Thanks for the insight Romulus, I've realised that situation often happens when one culture invades another, and the original language becomes taboo...

I tend to agree with Romulus or maybe the website used this sentence as an advertisement. If you spoke in a whisper no one would be able to hear you in English or any other language.