Is your feature request related to a problem? Please describe.
Noto Sans/Serif Thai doesn't seem to have neither italic nor oblique font style. Some application is not able to create the fake italic style, and might just use the normal one or even not allow the user to choose italic at all. For example, Affinity Designer shown below won't let the user choose the italic style at all.

Describe the solution you'd like
Create the Italic font style for both fonts.

Describe alternatives you've considered
Use some kind of tool to generate the fake italic style from the available font files.

Additional context