As I said in my follow-on post, the culprit is likely the WINE translation later. I don’t know if there’s a way to tell WINE to pick a different font for windows dialog boxes, but if there is, maybe picking a different font will help you.

Or maybe turning the checkmark on for Settings > Preferences > Searching > ☑ Use Monospaced font in Find dialog will help, because that will pick your monospaced font rather than the normal dialog font – and maybe that font has the Chinese glyphs you need.

Unfortunately, I have no experience with WINE, so I don’t have any more ideas.

The windows 7 should be fake due to WINE, it should be ubuntu20.04 LTS

What version of Notepad++ are you using?

Must be relatively recent as Find in Projects tab is in the Find window.
(Just stating this because I was about to ask if OP was using some ancient version when I noticed this.)

Given your screenshot, with the nine-dot icon where I’d expect a Windows “start menu”, and the linux penguin on the toolbar, I am wondering whether you are using Notepad++ on Ubuntu or other linux-based OS through WINE or equivalent; if so, you may be running into a limitation of the design decisions on WINE or equivalent when they translate win32-api calls to linux-compatible UI calls. (But this was just a guess, so if you’re really just in a highly-customized Windows OS, sorry for the misinterpretation.)

But you had already said,

I am using Notepad++ in Ubuntu desktop,

Sorry, by the time I wrote my reply, I forgot you’d said this. So yes, whatever font choices and translation between Notepad++.exe thru WINE into Ubuntu is getting messed up.

Please note that Ubuntu installer (which goes through WINE or equivalent) is not released by the developers; Notepad++ is a Windows OS application, and linux installations are not officially supported by the Notepad++ developers. The fellow users in this Community are happy to tell you how things should work in a true Windows environment, but we don’t necessarily have the expertise to answer all the oddities introduced by the WINE-or-equivalent translation layer.

It works for me. (I used google translate to generate some Chinese text, This is example text. => 这是示例文本。 for the document text and the FIND string, and It will be changed => 它会被改变 for the REPLACE string)

It properly matched and replaced for me, and displayed.

What version of Notepad++ are you using? (copy/paste your ? > Debug Info results here – mine are in my screenshot). Also, if your Notepad++ is new enough to have Settings > Preferences > Searching > ☐ Use Monospaced font in Find dialog checkbox, what is the state of that (or, better, paste in a screenshot of that whole page of settings)?

I tried seeing if the Settings > Style Configurator > Global Styles > Default Style would affect the Find/Replace dialog font, but it doesn’t; I don’t know what font is used in that dialog (probably a system font defined by your OS settings) – but maybe whatever font was chosen for that dialog on your machine doesn’t know the Chinese characters you are trying to use.

Given your screenshot, with the nine-dot icon where I’d expect a Windows “start menu”, and the linux penguin on the toolbar, I am wondering whether you are using Notepad++ on Ubuntu or other linux-based OS through WINE or equivalent; if so, you may be running into a limitation of the design decisions on WINE or equivalent when they translate win32-api calls to linux-compatible UI calls. (But this was just a guess, so if you’re really just in a highly-customized Windows OS, sorry for the misinterpretation.)