OK, here we run into a difficulty. I guess you are running the Chinese version of the operating system, whereas although my computers were bought in Xiamen, I’m running the British English version of the operating system, so your Chinese font names are in Chinese whereas mine are in Roman. I do not have the two fonts you mention, 微軟正黑體 and 王漢宗中黑體 under those names.
Interestingly, I don’t use FontBook, but Linotype FontExplorer X — originally it was a free app, I’m not sure now, as I haven’t upgraded for a long time — and Heiti TC and Heiti SC appear on that as alternate faces of ST Heiti Light and ST Heiti Regular (花纹黑体).
Anyway, I’ve copied a Chinese text — originally imported from Chinese WinWord, admittedly — into Nisus Writer Pro — gives you a character count — changed the font to Heiti TC, made sure I had a “paragraph” 250 characters and then added some English to the beginning … no problem.
I then opened a new document, set it to Chinese text, character Heiti TC, though my input system uses Simplified Chinese, typed a Roman ‘a’, then typed a Chinese string 我是英国人 enough times to take the paragraph count to 256 characters and then put in a paragraph break. No problem at all.
I then went back to the beginning of the paragraph and typed in more roman characters — abracadabra — and no corruption anywhere; leaving those in place, I inserted more Chinese — 好奇怪 — in the middle of the paragraph … no problems at all.
So, I don’t know what can be going wrong with your set-up or Birdy’s, other than possibly corrupt fonts or corrupt font-cache — someone more computer-savvy than me can advise you better how to deal with that.
By the way, Scrivener and Nisus Writer Pro both use the same text-engine released by Apple of which TextEdit is the vanilla showcase; on the other hand, Apple use another proprietary text-engine of their own for Pages, but which they aren’t releasing to developers. So it’s not surprising if Pages behaves differently to Scriv and TextEdit. See many, many threads which mention both these matters.

Mark