...I found out that if the Show Indic Options is enabled BEFORE I paste text with combining acute symbol (often used to mark stressed sounds) into Ai, these get displayed fine... but not if I paste first and enable the option after.

A related problem:
Copy-pasted text don’t show ö,ü,ä,õ letters
http://illustrator.uservoice.com/forums/601447/suggestions/40545004

Related discussions:
https://typedrawers.com/discussion/4254/precomposed-glyphs-not-defined-by-unicode-in-illustrator-and-photoshop-cc-2020
https://community.adobe.com/t5/illustrator-discussions/unable-to-display-combining-unicode-characters/m-p/13600450

I have the same problem on Windows 11 and Desktop Illustrator. For me, the diacritical marks over Cyrillic letters vanish: if I paste a text string containing и́ (that is и + ◌́), I obtain и, even if the font can display the combination perfectly well elsewhere. It also occurs with other diacritical marks even with Latin-alphabet letters. As well, there is a duplicate issue (”Diacritical characters are displayed incompletely”) stating the same essential problem that even includes a workaround in the comments.

A simple solution involving selecting the “Show Indic Options” (as detailed on https://www.behance.net/gallery/124447049/Javascript-for-Illustrator-ShowAnyGlyphs) solves the problem.

Very interesting.
I still can’t grasp why it works in some cases and do not in others...
Can you please share all test strings you used, and the file you used. The link to the video you mention could help too. The font I am able to get.

Thank you for responding!

I'm afraid that's not the case, however. The font itself has all the letters I need.
I did some more testing and even Arial as well as all other fonts I tried had the same result... (My font: Louis George Café)

But here's the kicker: If I just put the special letters in a text box without anything else, it works!
I'm beyond confused now. On their own the Umlaute are fine, in a text they and neighboring letters are left out.

(Just on the side - using the same Variable for multiple objects also runs into an error for me and many people, according to a YouTube-Tutorial. It says something like "The filter can't be run completely due to an unknown error.")

Saskia, I believe it depends on font, rather than the engine. If the font does not have diacritics, Illustrator has nowhere to get them from.
What font is this?

Specifically when working with variables in text form. They are not being imported correctly, despite everything else working. See picture.

I found out that combined diacritical characters are only displayed if there is a TAB, CR or FF in front of the character. Also, for many of the characters that are in the Unicode block U+0300 to U+036F, there are alternative separate characters. Unfortunately, Illustrator does not display these.

Therefore, I have now written a small Javscript that bypasses the problem. See https://www.behance.net/gallery/124447049/Javascript-for-Illustrator-ShowAnyGlyphs

I create fonts and need diacritical marks above or below letters for European fonts. When I copy the following text
́ ˘ ̧ ̒ ̋ ̏ ̀ ̌ ̦ ̊ ̄ · ̨ ̣ ̇ ̷ ̃ ̈ ^
from TextEdit (Mac) into Adobe Illustrator 25.3.1 (Mac), many of the characters disappear.
The problem does not occur in Affinity Designer. So please repair this bug, thanks.

HINDI / ARABIC SPEAKERS PLEASE HELP! Theres a huge problem or bug in illustrator i think... After I inputted the Diacritics (not full letters but symbols) for Arabic / Hindi (Devanagari) , I could not edit them. The type box for these Diacritical marks automatically disappear and can not change / edit / move them afterwards. This doesn't happen with other letters in the Arabic / Devanagari script hat are not diacritical marks - which i could select, move and edit on AI... (notice the messy Arabic diacritical marks on keys Q-W-E-R-T which i could not edit, and on keys like ZCFQERUM for hindi diacritics vowel markers

When I type or past the word "Dàmakɔ̀" in Illustrator CC 2019 it appears on the page as "Dàmakɔ", please help.

Illustrator does not display acute mark for cyrillic characters. I can copy and paste something like "коты́" from EditText or from web browser, but in illustrator document acute will not displayed no matter which font will be used.

This is very strange bug, because acute marks works in font selector preview (see screenshot)

iMac Retina 5K 27" late 2015, macOS 10.14.3, 4Ghz i7 32Gb Rum, AMD Radeon R9 M395X 4Gb.
AI v23.0.1