They won't let passengers who doesn't understand Mandarin sit in emergency rows. But F.A's flying international routes should have basic English ability to serve the passengers. On domestic routes, especially to smaller cities I don't see why F.As need to have great English skills if majority of the passengers are Chinese.
They don't need to have great English skills, but they have to speak the minimum at least able to communicate to one that don't speak mandarin.
By completely ignoring the importance of English, that only shows the airline have low quality, poor training, poor qualification for front line employees representing the company.
Japanese wasn't particular speak good english, but I believe all JL and NH flight attendants require to have a bachelor degree preferrably in English.