fix(translations): improve translation merger CLI and sync missing UI strings across locales (#5309)

# Description of Changes

This pull request updates the Arabic translation file
(`frontend/public/locales/ar-AR/translation.toml`) with a large number
of new and improved strings, adding support for new features and
enhancing clarity and coverage across the application. Additionally, it
makes several improvements to the TOML language check script
(`.github/scripts/check_language_toml.py`) and updates the corresponding
GitHub Actions workflow to better track and validate translation
changes.

**Translation updates and enhancements:**

* Added translations for new features and UI elements, including
annotation tools, PDF/A-3b conversion, line art compression, background
removal, split modes, onboarding tours, and more.
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* Improved and expanded coverage for settings, security, onboarding, and
help menus, including detailed descriptions and tooltips for new and
existing features.
[[1]](diffhunk://#diff-460d5f61a7649a5b149373af2e52a8a87d9a1964cf54240a78ad4747e7233effR442-R460)
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**TOML language check script improvements:**

* Increased the maximum allowed TOML file size from 500 KB to 570 KB to
accommodate larger translation files.
* Improved file validation logic to more accurately skip or process
files based on directory structure and file type, and added informative
print statements for skipped files.
* Enhanced reporting in the difference check: now, instead of raising
exceptions for unsafe files or oversized files, the script logs warnings
and continues processing, improving robustness and clarity in CI
reports.
* Adjusted the placement of file check report lines for clarity in the
generated report.

**Workflow and CI improvements:**

* Updated the GitHub Actions workflow
(`.github/workflows/check_toml.yml`) to trigger on changes to the
translation script and workflow files, in addition to translation TOMLs,
ensuring all relevant changes are validated.

These changes collectively improve the translation quality and coverage
for Arabic users, enhance the reliability and clarity of the translation
validation process, and ensure smoother CI/CD workflows for localization
updates.

<img width="654" height="133" alt="image"
src="https://github.com/user-attachments/assets/9f3e505d-927f-4dc0-9098-cee70bbe85ca"
/>


---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

scripts/translations/README.md

@@ -171,9 +171,15 @@ Merges missing translations from en-GB into target language files and manages tr
 
 **Usage:**
 ```bash
+# Operate on all locales (except en-GB) when language is omitted
+python scripts/translations/translation_merger.py add-missing
+
 # Add missing translations from en-GB to French
 python scripts/translations/translation_merger.py fr-FR add-missing
 
+# Create backups before modifying files
+python scripts/translations/translation_merger.py fr-FR add-missing --backup
+
 # Extract untranslated entries to a file
 python scripts/translations/translation_merger.py fr-FR extract-untranslated --output fr_untranslated.json
 
@@ -183,15 +189,20 @@ python scripts/translations/translation_merger.py fr-FR create-template --output
 # Apply translations from a file
 python scripts/translations/translation_merger.py fr-FR apply-translations --translations-file fr_translated.json
 
+# Override default paths if needed
+python scripts/translations/translation_merger.py fr-FR add-missing --locales-dir ./frontend/public/locales --ignore-file ./scripts/ignore_translation.toml
+
 # Remove unused translations not present in en-GB
 python scripts/translations/translation_merger.py fr-FR remove-unused
 ```
 
 **Features:**
 - Adds missing keys from en-GB (copies English text directly)
+- Runs across all locales for add-missing/remove-unused when language is omitted
 - Extracts untranslated entries for external translation
 - Creates structured templates for AI translation
-- Applies translated content back to language files
+- Applies translated content back to language files (template format or plain JSON)
+- Supports `--backup` on mutating commands
 - Automatic backup creation
 - Removes unused translations not present in en-GB