Thai characters with multiple vowels/tone marks overlap and render incorrectly

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Account name

tancoding

Account config

No response

Current Behavior

When typing in Thai, some characters with multiple vowels or tone marks—such as "เฮี้ยบ"—are rendered incorrectly. Specifically, the vowel and tone mark in "ฮี้"

overlap each other and appear stacked in a broken way. This makes the text hard to read.

This issue occurs with the Thai font "Boon", but I have also tested with several other Thai fonts and encountered the same issue.

I have tested on both Microsoft Edge and Google Chrome, and the issue occurs on both browsers.

Expected Behavior

Thai characters with multiple diacritics should render correctly, without overlapping or stacking incorrectly.

Steps To Reproduce

1. Open Monkeytype on Windows OS.
2. Set input language to Thai.
3. Start typing Thai words that include stacked vowels or tone marks, e.g., "เฮี้ยบ".
4. Observe the rendering issue in the word "ฮี้".

Environment

• OS: Windows 11
• Browser: Chrome / Edge (latest versions)
• Fonts tested: Boon(ไทย), and other fonts
• Issue persists across different browsers and fonts

Anything else?

No response

No source file, test, or entry point is named in the issue. First reproduce the Thai rendering problem on Windows 11 in Chrome or Edge using "เฮี้ยบ" and inspect the frontend rendering path; done means stacked vowels and tone marks render correctly across the tested Thai fonts and browsers.