It seems "()" and the sentence inside it are hiding on Hovercards, but some languages in Asia use "（）" as brackets, so let's support it to make Hovercards more useful in these languages.
Topic on Talk:Page Previews
Add the feature to hide "（）" as "()"
@Fitonay, could you please post a link to a Chinese Wikipedia page that isn't displaying usefully, as an example?
For the first article, I went to https://zh.wikipedia.org/wiki/中華民國#.E7.B6.93.E6.BF.9F and hovered over the link to that article in the caption. I see this text:
台北101（TAIPEI 101）是位於中華民國臺北市信義區的摩天大樓，樓高509.2米（1,671英尺），地上樓層共有101層、另有地下5層，總樓地板面積37萬4千平方公尺，由李祖原聯合建築師事務所設計、KTRT團隊与韩国三星物产（Samsung C&T）承造,
Do you see something else? Do you want to see something else?
I mean Hovercards seem to hide the brackets. For example, first paragraph of Amis language article is:
Amis is the Formosan language of the Amis (or Ami), an indigenous tribal people living along the east coast of Taiwan (see Taiwanese aborigines). Currently the largest of the Formosan languages, it is spoken from Hualien in the north to Taitung in the south, with another population near the southern end of the island, though the northern varieties are considered to be separate languages.
But on the Hovercards, it shows:
Amis is the Formosan language of the Amis, an indigenous tribal people living along the east coast of Taiwan. Currently the largest of the Formosan languages, it is spoken from Hualien in the north to Taitung in the south, with another population near the...
So the Hovercards of 台北101 could be:
I did not get " 台北101是位於中華民國臺北市信義區的摩天大樓，" in the Hovercards of 台北101. I actually got " 台北101（TAIPEI 101）是位於中華民國臺北市信義區的摩天大樓，" in the page preview.
The Page Preview looked like this:
Do you see the "（TAIPEI 101）" part in the first line, when you go to the same article and hover to get the preview for this article? Or is that missing for you?
Yes. But it doesn't show in most of other language and I think that is one of the Hovercards feature!
(Did you see the different between Amis article and Amis Hovercards?)
At the English Wikipedia, when I get the card for Amis, I don't see the text in parentheses. I wonder why that is?
@Fitonay is correct: the removing of text in parentheses is an intentional feature meant to make the preview text more useful (by removing things like alternate names, pronunciations, unit conversions, and so on). This happens on English, but, as they point out, not on Chinese and other East Asian languages because the parentheses characters are different.
Seems like a very useful report—it should be very easy for the development team to fix :)
Maybe it is the way to show up more information with priority for the reader at the start. The original text, pronunciation, synonym and conversion may not be the most important information in the page preview. So hide the text in parentheses can spare Hovercards space for other information.