feat(cli): add fern docs translation generate command for interactive i18n setup

[dsinghvi]

Description

Add a new fern docs translation generate command that interactively sets up internationalization for Fern documentation sites.

Changes Made

• Added docsTranslate.ts — core command that detects existing translations/languages config, prompts for default and target languages, updates docs.yml, and creates translations/<lang>/ directories
• Registered fern docs translation generate subcommand in cli.ts (nested command group)
• Supports 15 languages with native-script display names
• Handles fresh setup, existing translations config, and legacy languages field
• Rich formatted logging with progress indicators and next-step guidance
• Fixed regex to properly capture multi-line YAML translation entries (e.g., entries with default: true continuation lines)
• Updated changelog entry

Testing

• Local compilation (94/94 tasks pass)
• Lint and format checks pass
• Interactive flow tested with fresh docs.yml (no existing translations) — prompts for default language + target languages, updates YAML, creates directories
• Interactive flow tested with existing translations block (en + ja, adding ko) — detects existing config, skips default prompt, only offers remaining languages, merges correctly
• Verified docs.yml output correctness in both scenarios
• Verified translation directories created correctly

Link to Devin session: https://app.devin.ai/sessions/ccd7fd9e45ce416287a246d4a0a31b51
Requested by: @dsinghvi

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[graphite-app]

The regex pattern doesn't correctly match multi-line YAML list items. The pattern (?:\s+-[^\n]*\n?)* only matches lines that start with a dash (-), but YAML list items can have additional indented properties without dashes (like default: true).

For example, this existing block:

translations:
  - lang: en
    default: true
  - lang: es

Would only match up to - lang: en\n, stopping at default: true because it lacks a dash. This causes incomplete replacement, leaving orphaned YAML and corrupting the docs.yml file.

Fix: Use a more comprehensive regex that matches the entire YAML block:

const translationsRegex = /^translations:\s*\n(?:(?:  |\t)+-[^\n]*\n(?:(?:    |\t\t)+[^\n]+\n)*)*(?=\S|$)/m;

Or use a YAML parser library to safely manipulate the structure instead of regex replacement.

Suggested change

	const translationsRegex = /^translations:\s*\n(?:\s+-[^\n]*\n?)*/m;
	if (translationsRegex.test(rawContent)) {
	return rawContent.replace(translationsRegex, translationsBlock + "\n");
	const translationsRegex = /^translations:\s*\n(?:[ \t]+[^\n]*\n?)*/m;
	if (translationsRegex.test(rawContent)) {
	return rawContent.replace(translationsRegex, translationsBlock + "\n");

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[devin-ai-integration]

E2E Test Report

Both tests passed after fixing a bug found during testing.

Bug Found & Fixed

The regex in updateDocsYamlContent (/^translations:\s*\n(?:\s+-[^\n]*\n?)*/m) only captured lines starting with - (dash lines) but not continuation lines like default: true. This caused partial replacement when existing translations had multi-line entries, resulting in duplicate/malformed YAML output. Fixed with a simpler regex that captures all indented lines under the translations: key.

Test Results

Test	Result
Fresh docs.yml (no existing translations)	Passed
Existing translations (en + ja, adding ko)	Passed

Test 1: Fresh docs.yml

Setup: Minimal fern project with docs.yml containing only instances: [] and navigation.

Assertions:

• Command reachable at fern docs translation generate — passed
• Header "🌐 Fern Docs — Internationalization Setup" displayed — passed
• Prompted "Is English your default documentation language?" — passed (answered Yes)
• Checkbox prompt for target languages appeared — passed (selected Spanish, French)
• docs.yml updated with correct translations block — passed:

  translations:
    - lang: en
      default: true
    - lang: es
    - lang: fr

• translations/es/ and translations/fr/ directories created — passed
• Summary with "Internationalization setup complete!" and next steps displayed — passed

Test 2: Existing translations

Setup: Fern project with docs.yml containing existing translations: block with en (default) and ja.

Assertions:

• "Existing translations detected: English, Japanese" displayed — passed
• "Default language: English" displayed — passed
• Did NOT prompt for default language (already set) — passed
• Checkbox did NOT include English or Japanese — passed (selected Korean)
• docs.yml correctly merged all languages — passed:

  translations:
    - lang: en
      default: true
    - lang: ja
    - lang: ko

• Only translations/ko/ directory created (not ja) — passed

Devin session