FYI, Hebrew also have the so called “diacritics” which are part of many scripts, even the Latin-1! The German “umlaut” ones, the french “circumflex” as well as various Polish, Turkish and many more languages.
Hebrew in particular has many of these. My experience with previous EE versions (I didn’t upgrade to v.13 yet) tells me that it displays some right but many more not so. Even some of the European, Latin-1 diacritics are not displayed right, e.g., ĉb (small Latin ‘c’ U+0063 + Combining Circumflex Accent U+0302 and then small Latin letter ‘b’) are displayed ‘c’ and above it the Circumflex (correct!) then a space (not correct!) and then the ‘b’.
BTW, all of it was tried using the UTF-8 encoding.
Are you using a specialized Thai encoding (Hebrew has four, in addition to the Unicode ones), or UTF-8?