Try changing the IDE appearance font to the one that can display Thai glyphs: https://stackoverflow.com/a/46388106/104891.

Or use 2018.3.1 (or later) from http://www.jetbrains.com/idea/download/index.html and add

-Dide.find.use.editor.font=true

in Help | Edit Custom VM Options and restart the IDE.

your solution does't solved my problem.

Did you try both of them? What IDE version do you use?

Which font did you set for IDE UI and for the Editor?

Yes.

With your current settings this font will be used for Find field:

Make sure it can display Thai glyphs.

In "Color Scheme Font",  can display Thai, but search box is not.

Please show the screenshot of the editor with the Thai glyphs. Did you restart IDE after editing .vmoptions file?

According to https://youtrack.jetbrains.com/issue/IDEA-106651, this feature should work since 2018.3.1.

Does it help if you change the -Dide.find.use.editor.font=true to -Dide.find.use.editor.font=false and restart IDE again?