[BUG] Model omits diacritical marks (accents) in non-English languages unless explicitly requested

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?

Any prompt written in a language that uses diacritical marks (e.g., Portuguese, French, Spanish). For example, asking Claude Code to write comments, commit messages, or respond in Portuguese.

When responding in languages that use diacritical marks (accents, tildes, cedillas, etc.), the model consistently omits them from words that require them. For example:

"nao" instead of "não"
"codigo" instead of "código"
"voce" instead of "você"
"tambem" instead of "também"
"e" instead of "é"
Accents are only placed correctly when the user explicitly asks the model to use them. This happens across all types of output: responses, code comments, commit messages, and file content.

What Should Happen?

The model should use correct diacritical marks by default when writing in any language that requires them, without the user needing to explicitly request proper orthography. Omitting accents changes meaning in many languages (e.g., in Portuguese, "e" means "and" while "é" means "is").

Error Messages/Logs

Steps to Reproduce

1. Open a project that uses internationalization (i18n) with translation files (e.g., JSON locale files).
2. Ask Claude Code to add or modify UI elements that require generating or updating translation strings in a non-English language that uses diacritical marks (e.g., Portuguese).
3. Example prompt: "Add a settings page with all labels in Portuguese"
4. Observe the generated translation/locale files — diacritical marks (accents, tildes, cedillas) will be missing from words that require them.

• Example: "notifications": "Notificacoes" instead of "notifications": "Notificações"
• Example: "schedule": "Agendamento de publicacao" instead of "Agendamento de publicação"

1. The only way to get correct accents is to explicitly instruct: "Use correct Portuguese accents in all strings."

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.90 (Vs Code extension)

Platform

Anthropic API

Operating System

Other Linux

Terminal/Shell

Other

Additional Information

_No response_