Fix CJK character display issues in Windows terminals

[Observer-GGboy]

Problem

OpenCode terminals on Windows do not properly display CJK (Chinese, Japanese, Korean) characters. Instead, they appear as gibberish, question marks, or cause encoding errors.

Affected Scenarios

1. Terminal Output

   $ echo "你好世界"
   ?????
   

2. Python Scripts

   $ python -c "print('你好')"
   UnicodeEncodeError: 'ascii' codec can't encode characters
   

3. Git Operations

   $ git status
   ?? "\346\226\346\231\230.md"
   

Root Cause

Windows historically uses GBK/GB2312 encoding by default, not UTF-8. This causes issues when:

• Terminal code page is not set to UTF-8 (CP65001)
• Environment variables (LANG, LC_ALL) are not configured
• Python's UTF-8 mode is not enabled
• Shell encoding (PowerShell/CMD) is not configured

Proposed Solution

Add platform-specific UTF-8 defaults for Windows PTY (pseudo-terminal) creation:

1. Environment Variables

   • Set LANG=en_US.UTF-8
   • Set LC_ALL=en_US.UTF-8
   • Set PYTHONUTF8=1 (Python 3.7+)
   • Set PYTHONIOENCODING=utf-8

2. Shell Startup Arguments

   • CMD.exe: Run chcp 65001 to set code page to UTF-8
   • PowerShell: Configure OutputEncoding and InputEncoding to UTF-8

Impact

• Target Platform: Windows only (no impact on macOS/Linux)
• User-Visible: Yes (fixes CJK character display)
• Backwards Compatible: Yes (only sets defaults, users can override via env parameter)

Related

• PR: fix(pty): Add UTF-8 defaults for Windows PTY #10489

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• OpenCode crashes during use on Windows (garbled console output) #10414: OpenCode crashes during use on Windows (garbled console output) - Similar garbled output on Windows
• Chinese Characters #10486: Chinese Characters - CJK characters appearing unexpectedly in output
• Garbled characters appear after launching the program on Windows system. #9814: Garbled characters appear after launching the program on Windows system
• Ctrl+C during response causes terminal to print endless garbage and become unresponsive #10265: Ctrl+C during response causes terminal to print endless garbage and become unresponsive - Related terminal encoding issue
• Scoop-fixes-opencode-windows-x64-garbled-output-issue-but-cause-unknown #10341: Scoop-fixes-opencode-windows-x64-garbled-output-issue-but-cause-unknown - Windows-specific garbled output issue
• 命令行模式下中文显示突然全部变成乱码 #9793: 命令行模式下中文显示突然全部变成乱码 (Chinese characters display as garbled in CLI mode) - CJK display issue on Windows
• Undo/revert fails for files with non-ASCII filenames on Windows #10210: Undo/revert fails for files with non-ASCII filenames on Windows - Related non-ASCII handling issue

Feel free to ignore if none of these address your specific case.