Add Japanese translation

[tkymmm]

Description

Add Japanese translation

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

🧪 How Has This Been Tested?

I confirmed it using Docker on my own server.

Checklist:

• Verified output manually
• Tested with relevant sample documents or data
• Wrote Vite Test Case (if applicable)

Expected Results:

All Japanese translations

Actual Results:

There were no items to translate in faq.html.

Checklist:

• I have signed the Contributor License Agreement (CLA) or my organization has signed the Corporate CLA
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

Summary by CodeRabbit

• New Features
  • Full Japanese localization added across the app: navigation, hero/marketing, settings, compliance, FAQ, support, footer, and onboarding copy.
  • Japanese translations for all PDF tools and workflows (compression, merge, convert, compare, signatures, builder, etc.) plus UI labels, messages, and templated strings.
  • Japanese is now selectable as a language option in the application.

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 7efa2f29-9875-41bb-a533-a04d634357b1

📥 Commits

Reviewing files that changed from the base of the PR and between e72df17 and dc87af9.

📒 Files selected for processing (1)

• public/locales/ja/tools.json

🚧 Files skipped from review as they are similar to previous changes (1)

• public/locales/ja/tools.json

---

📝 Walkthrough

Walkthrough

This PR adds Japanese language support by introducing two new locale JSON files (public/locales/ja/common.json, public/locales/ja/tools.json) and updating i18n and build/routing config to recognize and route /ja language-prefixed URLs.

Changes

Cohort / File(s)	Summary
Japanese Localization Files public/locales/ja/common.json, public/locales/ja/tools.json	Add comprehensive Japanese translation strings for UI sections and many tool-specific workflows (navigation, hero, features, tools, upload, compression, OCR, signatures, compare, visual workflow builder, etc.) with templated placeholders for runtime interpolation.
i18n Configuration src/js/i18n/i18n.ts	Add 'ja' to supportedLanguages, add ja: '日本語' to display names, and extend URL parsing / link-rewriting regexes to detect and handle the /ja prefix.
Build / Routing Config vite.config.ts	Include 'ja' in SUPPORTED_LANGUAGES and expand LANG_REGEX so requests under /ja/... are recognized by language routing middleware.

Sequence Diagram(s)

(omitted — changes are localization additions and minor routing/i18n updates that do not introduce new multi-component control flow requiring a sequence diagram)

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• add Russian translation #555 — Adds a Japanese locale and makes parallel i18n and build config edits affecting the same files and patterns.

Suggested reviewers

• alam00000

Poem

🐰 I hopped through keys and strings today,
小さな翻訳を運んで来たよ、明るい道で 🌸
Buttons now say hello in 日本語,
Pages hum softly with new script and cheer,
The rabbit nods — the UI speaks another ear.

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Add Japanese translation' clearly summarizes the main change: introducing Japanese localization to the project.
Description check	✅ Passed	The description covers the key required sections: identifies the change as a new feature, includes testing confirmation, and marks most checklist items. However, it lacks specific issue reference and testing detail.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

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[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

src/js/i18n/i18n.ts (1)

62-64: Consider generating regex from supportedLanguages to reduce maintenance burden.

The language list is hardcoded in three separate regex patterns (lines 63, 153, 246) in addition to the supportedLanguages array. Adding a new language requires updating four locations, which is error-prone.

♻️ Suggested refactor to DRY up language matching

+// Build regex pattern from supportedLanguages array
+const langPattern = supportedLanguages.join('|');
+
 export const getLanguageFromUrl = (): SupportedLanguage => {
   // ...
   const langMatch = path.match(
-    /^\/(en|ar|fr|es|de|zh|zh-TW|vi|tr|id|it|pt|nl|be|da|ko|sv|ru|ja)(?:\/|$)/
+    new RegExp(`^\\/(${langPattern})(?:\\/|$)`)
   );

Apply the same pattern to the regexes in changeLanguage (line 153) and rewriteLinks (line 246).

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@src/js/i18n/i18n.ts` around lines 62 - 64, Replace the hardcoded language
alternation in the regex used to detect language prefixes with a regex built
from the existing supportedLanguages array; specifically, generate an escaped
alternation string from supportedLanguages and use it to build the regex used
for langMatch (the path.match call), and reuse the same generated regex (or a
helper function that returns it) in changeLanguage and rewriteLinks so all three
places derive their pattern from supportedLanguages instead of duplicated
literals.

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@public/locales/ja/tools.json`:
- Around line 463-464: The translation for the JSON key "rightDocument" is
incorrect: it currently reads "正しい文書" (meaning "correct document") but should
indicate the right-side panel; update the value for "rightDocument" (paired with
"leftDocument") to a phrase like "右の文書" or "右側の文書" so it clearly means "right
side document" in the side-by-side PDF comparison UI.

---

Nitpick comments:
In `@src/js/i18n/i18n.ts`:
- Around line 62-64: Replace the hardcoded language alternation in the regex
used to detect language prefixes with a regex built from the existing
supportedLanguages array; specifically, generate an escaped alternation string
from supportedLanguages and use it to build the regex used for langMatch (the
path.match call), and reuse the same generated regex (or a helper function that
returns it) in changeLanguage and rewriteLinks so all three places derive their
pattern from supportedLanguages instead of duplicated literals.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 8b51a632-344d-4c26-92c8-61b6454df428

📥 Commits

Reviewing files that changed from the base of the PR and between 095d68d and e72df17.

📒 Files selected for processing (4)

• public/locales/ja/common.json
• public/locales/ja/tools.json
• src/js/i18n/i18n.ts
• vite.config.ts

[tkymmm]

I have read the CLA Document and I hereby sign the CLA