I have tried in both the English and Chinese Wikipedias, and I found that whenever I add a Chinese full stop "。" (without the quotations) after an inline citation, the "。" will disappear after the edit is saved. If you need an example, you can tell me, but basically, try putting "。" after <ref>(cite source)</ref> and see what happens.
Topic on VisualEditor/Feedback
I am referring to when you add the "。" after the citation and nothing follows it (e.g. at the end of a paragraph).
Thank you for your note, HYH.124. I apologize for this frustrating situation. User:User:DChan (WMF) will need to know about this problem.
Ping User:DChan (WMF) :)
I wasn't able to reproduce this when I pasted the full stop into my sandbox. However, perhaps it is just because I pasted it rather than typing it, or because I have a different computer. User:HYH124, could you please tell me what your web browser and operating system are, and how you are typing? These details sometimes make a big difference.
I have officially reported this problem as phab: T78122.
Thank you, again.