feat(i18n): Migrate to PO/MO translation system with French support

[bvisible]

Summary

This PR modernizes the internationalization (i18n) system by migrating from CSV to the industry-standard PO/MO format and adds complete French language support.

Key Changes

• PO/MO Translation System: Migrate from CSV to PO/MO format for better tooling support
• French Language: Add complete French translations (4900+ strings)
• Dynamic Language Detection: Auto-detect available languages from .po files
• Font Rendering Fix: Resolve special character display issues (e.g., "ê" in Português)

Features

1. PO/MO Translation Migration

• New translation files: ar.po, fr.po, pt_br.po
• Template file: main.pot for translators
• Removed deprecated CSV files
• Added migration script and documentation

2. Dynamic Language Configuration

• get_supported_locales() automatically scans .po files in locale directory
• When allowed_locales is empty in POS Settings, all available languages are shown
• No code changes needed when adding new languages

3. French Language Support

• Complete translation of all 4900+ strings
• Verified translation quality and variable preservation

4. Font Stack Fix

• Reordered font-family: Inter before SaudiRiyalSymbol
• Fixes rendering of accented characters (ê, é, à, etc.)

Files Changed

Category	Files
Backend API	pos_next/api/localization.py
Frontend	POS/src/composables/useLocale.js, POS/src/index.css
Translations	pos_next/locale/*.po, pos_next/locale/main.pot
Documentation	docs/Translation-Migration-Guide.md, docs/LOCALIZATION.md
CI/CD	.github/workflows/update-translations.yml
Scripts	scripts/migrate_translations.py

How to Add New Languages

1. Create a new .po file: pos_next/locale/{lang_code}.po
2. Add the language config in POS/src/composables/useLocale.js:

new_lang: {
  name: "Language Name",
  nativeName: "Native Name",
  countryCode: "xx",
  dir: "ltr", // or "rtl"
}

3. Translate the strings in the .po file
4. Run bench build --app pos_next

Testing

• Verified French translations display correctly
• Tested language switching between all 4 languages
• Confirmed special characters render properly
• Validated dynamic language detection works

[bvisible]

CI Failures Analysis

The 3 failing checks are pre-existing issues in the repository's CI configuration, not caused by this PR:

1. Server Build (❌)

ValueError: expected only letters, got ''
MO file created at .../pos_next.mo  ← Our translations compiled successfully

The error occurs during translation compilation of another app (not pos_next). Our French MO file was created successfully.

2. Frappe Linter (❌)

Pre-existing lint issues in the codebase:

• # -*- coding: utf-8 -*- declarations (UP009)
• from __future__ import unicode_literals (UP010)
• Trailing whitespace in various files

These issues exist in files that were not modified by this PR.

3. Vulnerable Dependency Check (❌)

ERROR: No matching distribution found for erpnext

The CI tries to install erpnext from PyPI, but ERPNext is a Frappe app, not a PyPI package. This is a CI configuration issue.

---

Conclusion: All 3 failures are unrelated to the i18n changes in this PR. The CI configuration needs to be fixed independently.

[engahmed1190]

Thank you, @bvisible, for your valuable contribution to the POSNext translations.
The implementation looks solid, and the quality is appreciated.
I will proceed with testing the changes across three additional languages.
Excellent work, and thank you for your effort and collaboration.