[BUG] Thai vowel "า" (sara aa) not rendering in Claude Code

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Thai vowel character "า" (U+0E32, THAI CHARACTER SARA AA) does not render in Claude Code terminal sessions, while it displays correctly in normal terminal sessions outside of Claude Code. This makes typing Thai text extremely difficult as the user cannot see what they're typing.

The same Thai text displays perfectly in:

• Normal terminal (before running claude)
• Other terminal applications
• Text editors

What Should Happen?

Thai text should render correctly with all characters visible, including the "า" vowel, just as it does in a normal terminal session.

Example of what should be visible:

• สวัสดี (hello)
• ครับ (polite particle)
• อา (vowel aa)

Error Messages/Logs

Steps to Reproduce

1. Launch iTerm2 with Thai font support (Thonburi configured as Non-ASCII font)
2. Start Claude Code: claude
3. Type Thai text containing the vowel "า", for example: "สวัสดี" (hello) or "ครับ" (polite particle)
4. Observe the rendering

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.23

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

Additional Context

• This issue has persisted across multiple sessions and restarts
• The user has tried:
• Different font configurations
• Enabling/disabling Unicode normalization
• Using different terminal emulators
• Multiple restarts of both terminal and Claude Code
• The character IS being received by Claude (the AI can read it), but it's not being rendered visually for the user
• This appears to be a rendering issue specific to how Claude Code handles certain Thai combining characters or cursor positioning with Thai text

Environment

• OS: macOS Darwin 25.2.0
• Terminal: iTerm2
• Claude Code Version: 2.1.23 (based on last release notes seen)
• Fonts:
• Normal Font: Menlo-Regular 13
• Non-ASCII Font: Thonburi 12 (Thai font bundled with macOS)
• Locale: en_US.UTF-8
• TERM: xterm-256color
• Unicode Settings:
• Use Non-ASCII Font: Enabled
• Unicode Normalization: Enabled (tried both enabled and disabled)