[Qt5]How to change the Font in Linguist?

hi,

I have meet some trouble when porting from Qt4 to Qt5, one thing is the font in linguist cannot show every word well

I am translating a same .ts file from English to Chinese, when using linguist in Qt4, it use the font setting the same as my system
Attachment 9051

but when using linguist in Qt5, it seem to use a fixed font
Attachment 9052

I am sure this problem is due to the setting of font. Because when developing my own application, I meet the same problem and solve it by changing the font of QApplication

Is there some way to change font of linguist without modifying the source of Qt?

My OS is Ubuntu 12.04.

Thanks for your help!