As mentioned by cocoanetics
http://www.cocoanetics.com/2012/12/radar-uitextview-ignores-minimummaximum-line-height-in-attributed-string/ (I can reproduce it on iPhone 5 with iOS 6.1.2)
Because there is a bug in UITextView, I had no way to adjust the line spacing of text. It should be ok for english, however chinese is not good enough.
So I had the following trick,
When user switches to chinese, I set “Euphemia UCAS” as default font, but displays chinese text as normal in UITextView. I found that “line-spacing” will be inherited from “Euphemia UCAS”.