Thai vowel characters (Sara) not rendering correctly in terminal (iTerm2/macOS)

Description

Thai characters, specifically certain vowels (สระ), are not displaying correctly in Claude Code terminal output. The issue affects both user input prompts and Claude's responses.

Environment

• OS: macOS (Darwin 25.2.0)
• Terminal: iTerm2
• Shell: zsh
• Claude Code version: 2.1.29
• Terminal encoding: UTF-8
• Locale:

``
LANG="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_CTYPE="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
``

Problem Details

The Thai vowel character Sara AA (สระ อา) and potentially other vowels are not rendering correctly:

| Dec | Hex | Character | Unicode Name |
|-----|-----|-----------|--------------|
| 210 | 0xD2 | า | THAI CHARACTER SARA AA (U+0E32) |

Example:

• Expected: สวัสดี (sa-wat-dee)
• Actual: vowel characters missing or not displayed

Steps to Reproduce

1. Launch Claude Code in iTerm2
2. Type a prompt in Thai, e.g., อธิบายเรื่องนี้เป็นภาษาไทย
3. Observe that certain vowel characters are missing in both the input display and Claude's response

Expected Behavior

All Thai characters including vowels (สระ) should render correctly:

• สระ อา (า)
• สระ อี (ี)
• สระ อู (ู)
• วรรณยุกต์ (tone marks)
• etc.

Actual Behavior

Vowel characters are dropped or not displayed, making Thai text difficult to read.

Additional Context

• This issue may be related to how Claude Code handles Unicode Thai character rendering
• iTerm2 displays Thai correctly in other terminal applications (vim, cat, echo)
• The issue appears specific to Claude Code's terminal rendering layer

Workaround Attempted

• [x] Verified iTerm2 font supports Thai
• [x] Confirmed UTF-8 encoding in terminal preferences
• [x] Tested with different fonts - issue persists