gh-subtitle

README

🌐 gh-subtitle

gh-subtitle is a GitHub CLI (gh) extension that translates PR / Issue / Discussion bodies and comments, appending translated text as subtitles.

It uses the Copilot SDK to translate content and manages translation blocks with HTML comment markers for idempotent updates.

Usage

# Add Japanese translation to a PR
$ gh subtitle https://github.com/owner/repo/pull/123 -t ja

# Add English translation to an Issue
$ gh subtitle https://github.com/owner/repo/issues/456 -t en

# Add both Japanese and English translations (mutual translation)
$ gh subtitle https://github.com/owner/repo/pull/123 -t ja -t en

# Translate only the body (skip comments)
$ gh subtitle https://github.com/owner/repo/pull/123 -t ja --body-only

# Preview translations without updating GitHub
$ gh subtitle https://github.com/owner/repo/pull/123 -t ja --dry-run

# Remove all translation blocks
$ gh subtitle https://github.com/owner/repo/pull/123 --clear

# Remove only Japanese translation blocks
$ gh subtitle https://github.com/owner/repo/pull/123 --clear -t ja

# Use a different model
$ gh subtitle https://github.com/owner/repo/pull/123 -t ja -m copilot:gpt-4o

Supported Content

Type	Body	Comments
Pull Request	✓	Issue comments, Review comments
Issue	✓	Issue comments
Discussion	✓	Comments, Replies

Translation Markers

Translations are inserted at the end of each content item, wrapped in HTML comment markers:

Original content...

<!-- subtitle:ja:start sha256:a1b2c3d4 -->
---
<sub>🌐 Translated by [gh-subtitle](https://github.com/k1LoW/gh-subtitle) (model: copilot:gpt-4o-mini)</sub>

日本語翻訳...
<!-- subtitle:ja:end -->

• Language-scoped markers — Each language gets its own marker block (<!-- subtitle:ja:... -->, <!-- subtitle:en:... -->), allowing multiple translations to coexist.
• Hash-based change detection — A SHA256 hash of the original text is embedded in the start marker. Re-running the command skips items whose original text hasn't changed.
• Idempotent updates — Running the same command multiple times is safe; existing translations are updated in place rather than duplicated.

Install

$ gh extension install k1LoW/gh-subtitle

Prerequisites

• GitHub Copilot CLI >= 0.0.411 (copilot --version to check, copilot update to upgrade)

Authentication

Local

By default, gh-subtitle uses the logged-in user's authentication via the gh CLI (i.e., gh auth login). No additional configuration is needed.

GitHub Actions / CI

For CI environments, set a token via environment variables:

Environment Variable	Description
GH_SUBTITLE_COPILOT_TOKEN	Token for Copilot SDK authentication (highest priority)
GITHUB_TOKEN	Fallback token for Copilot SDK authentication

Token resolution order: GH_SUBTITLE_COPILOT_TOKEN → GITHUB_TOKEN → logged-in user (via gh auth).

Note: The gh CLI uses GH_TOKEN or GITHUB_TOKEN for GitHub API operations independently.

# Example GitHub Actions step
- run: gh subtitle ${{ github.event.pull_request.html_url }} -t ja
  env:
    GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
    GH_SUBTITLE_COPILOT_TOKEN: ${{ secrets.COPILOT_TOKEN }}

Command Line Options

Option	Short	Description
--translate	-t	Target language(s) for translation (required, can be specified multiple times)
--model	-m	Model to use in <provider>:<model_name> format (default: copilot:gpt-4o-mini)
--dry-run	-n	Show translations without updating GitHub
--body-only		Translate only the body (skip comments)
--clear		Remove translation marker blocks (all languages, or specific languages with -t)
--include-bots		Include bot comments in translation (skipped by default)

Contributing

To use this project from source, instead of a release:

go build .
gh extension remove subtitle
gh extension install .

Documentation

Overview

Copyright © 2026 Ken'ichiro Oyama <k1lowxb@gmail.com>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.