This is a bug that was present before iOS 6, the Chinese glyphs in the following line would be bold if the locale was set to Chinese due to an incorrect entry in the global font cascade table. Filed as rdar://11262229
English and 中文 -- Chinese characters
东方盖饭
东方盖饭
Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla
Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla Bla bla