I’m having font problems, or maybe character encoding on wordpress.

I am building a Thai website, most of the articles are in the correct language and there is no problem.

But there are a number of articles posted when posting errors in the article letters.

Such as:
https://prnt.sc/vswh8j or https://prnt.sc/vswi15

As in the picture I have given, some of the first characters can be Thai, but the following characters are like: "ี่๠€ ภ£ ๠‡ วà¸" and I don’t translate get it in any language.

I don’t think my source code supports Thai or something like that. I have tried researching on this problem a lot and tried many ways but to no avail.

Hope you can guide me to fix it. Thank you very much