microsoft · VAsHachiRoku · Jul 31, 2026 · Jul 31, 2026 · Jul 31, 2026 · Jul 31, 2026
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -7,6 +7,18 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [1.2.2] - 2026-07-31
+
+### Added
+- **English-language enforcement (#23)**: `Test-TierModelPrerequisites` now fails fast — before any deployment or audit change — when the environment is not English (`en-US`). Two unconditional checks run up front and are inherited by both `Deploy-TierModel.ps1` and `Audit-TierModel.ps1`:
+  - **Host operating system** — reads the local machine's static `InstallLanguage` LCID (`HKLM\SYSTEM\CurrentControlSet\Control\Nls\Language`) and requires an English variant (primary language `0x09`, e.g. en-US/en-GB). Runs after the elevation check and **before** the Pester/module checks, and returns immediately on a non-English host so the operator is never asked to install modules on an unsupported OS.
+  - **Active Directory** — resolves three well-known groups by SID (Domain Admins `<DomainSID>-512`, Server Operators `S-1-5-32-549`, Account Operators `S-1-5-32-548`) and requires each directory `Name` to be its English value. Child-domain safe (no Enterprise/Schema Admins); names are read from AD (never client-side SID translation, which the local OS would localize into a false pass). A confirmed localized name always fails closed even if another well-known group cannot be resolved.
+  - Both checks emit friendly `Errors`/`Remediation` and record diagnostics in `EnvironmentSnapshot` (`HostInstallLanguage`, `HostOsEnglish`, `AdLanguageEnglish`, `AdLanguageMismatches`, …).
+- **Documentation**: new `docs/language-support.md` documenting the English-only requirement, the 18 fully-localized Windows Server languages that are detected and stopped, and a future community-localization roadmap. Prerequisite notes added to the README, the quick/detailed deployment guides, and the FAQ.
+
+### Notes
+- No configuration changes are required and English (`en-US`) deployments and audits are unaffected (full suite: **1,435** automated tests passing; module scope ~91% coverage). Non-English environments are a documented, unsupported scenario — see `docs/language-support.md`.
+
 ## [1.2.1] - 2026-07-30
 
 ### Fixed

diff --git a/README.md b/README.md
@@ -31,30 +31,32 @@ To get started with TierModel, please refer to our comprehensive documentation:
 - **[CI/CD Integration](https://microsoft.github.io/ActiveDirectoryTierModel/ci-cd/)** - Pipeline integration and automation
 - **[Test Tag Matrix](https://microsoft.github.io/ActiveDirectoryTierModel/test-tag-matrix/)** - Pester test organization
 - **[Test Coverage](https://microsoft.github.io/ActiveDirectoryTierModel/test-coverage/)** - Comprehensive test coverage analysis and roadmap
+- **[Language Support](https://microsoft.github.io/ActiveDirectoryTierModel/language-support/)** - Supported languages (English only today) and the localization roadmap
 
 ### 🔧 Technical Specifications
 - **[Feature Specification](specs/001-tier-model-module/spec.md)** - Complete requirements and user stories
 - **[Implementation Plan](specs/001-tier-model-module/plan.md)** - Technical architecture and design decisions
 
 ## 🧪 Testing & Quality Assurance
 
-**Current Test Status: ✅ ALL TESTS PASSING** *(Last run: July 30, 2026)*
+**Current Test Status: ✅ ALL TESTS PASSING** *(Last run: July 31, 2026)*
 
 | Test Suite | Test Files | Test Cases | Status | Coverage |
 |------------|-----------|------------|--------|----------|
-| **Unit Tests** | 17 files | 1,137 tests | ✅ 100% Pass | **88.68%** |
+| **Unit Tests** | 17 files | 1,147 tests | ✅ 100% Pass | **88.72%** |
 | **Integration Tests** | 7 files | 288 tests | ✅ 100% Pass | **100%** |
 | **Manual Integration Tests** | 1 file | 331 tests | ✅ 100% Pass | **100%** |
-| **Total** | **25 files** | **1,756 tests** | ✅ **All Passing** | **88.68%** |
+| **Total** | **25 files** | **1,766 tests** | ✅ **All Passing** | **88.72%** |
 
 ### Test Coverage Highlights
 - ✅ **63/63** production files have comprehensive test coverage (5 new Windows LAPS cmdlets added in v1.2.0)
-- ✅ **100%** of all automated 1,425 test cases passing
+- ✅ **100%** of all automated 1,435 test cases passing
 - ✅ **100%** of all manual 331 test cases passing
-- ✅ **88.68%** overall docs-scope line coverage — `modules/TierModel/*` module scope ~91% (all above 80% CI gate); `Audit-TierModel.ps1` at 73.1% (new fail-fast/alignment paths need live-AD or PS<7 to exercise), `Deploy-TierModel.ps1` at 81.4%
+- ✅ **88.72%** overall docs-scope line coverage — `modules/TierModel/*` module scope ~91% (all above 80% CI gate); `Audit-TierModel.ps1` at 73.1% (new fail-fast/alignment paths need live-AD or PS<7 to exercise), `Deploy-TierModel.ps1` at 81.4%
 - ✅ `Get-TierModelConditionalGroupNames` — new function with full test coverage (6 unit tests)
 - ✅ **New in v1.2.0:** Unit and integration test files for Windows LAPS (Unit.WinLapsAclOperations.Tests.ps1, Integration.WinLapsDeployment.Tests.ps1)
 - ✅ **New in v1.2.1:** UI & reliability bug fixes (BUG-001..011) — see CHANGELOG.
+- ✅ **New in v1.2.2:** English-language enforcement (#23) — fail-fast host-OS and Active Directory (en-US only) prerequisite checks (10 new unit tests); see [Language Support](https://microsoft.github.io/ActiveDirectoryTierModel/language-support/).
 - ✅ Mock-based testing (no Active Directory connectivity required)
 - ✅ WhatIf support validation across all deployment operations
 
@@ -138,6 +140,7 @@ cd ActiveDirectoryTierModel
 - **Elevation**: Administrator privileges required
 - **Domain Admin**: Membership in Domain Admins group
 - **Modules**: ActiveDirectory, GroupPolicy (see `config/dependencies.json`)
+- **Language**: English (`en-US`) only — both the **host OS** (the machine you run the scripts from) and **Active Directory** must be English (see [Language Support](https://microsoft.github.io/ActiveDirectoryTierModel/language-support/))
 
 *For detailed prerequisite validation, run `Test-TierModelPrerequisites`*
 
@@ -150,7 +153,7 @@ cd ActiveDirectoryTierModel
 
 ---
 
-**Version**: 1.2.1 | **License**: MIT | **Status**: ✅ Production Ready
+**Version**: 1.2.2 | **License**: MIT | **Status**: ✅ Production Ready
 
 ## 🚀 Releasing
 

diff --git a/docs/detailed-deployment-guide.md b/docs/detailed-deployment-guide.md
@@ -4,6 +4,8 @@ This guide provides a step-by-step deployment workflow using scoped deployment p
 
 For a streamlined full deployment workflow, see the [Quick Deployment Guide](quick-deployment-guide.md).
 
+> **Supported environment:** English (`en-US`) only — the **host OS** (the machine you run the scripts from) and **Active Directory** must both be English. Non-English environments are detected and stopped during prerequisite validation. See [Language Support](language-support.md).
+
 ## Overview
 
 This detailed approach deploys Tier Model components one type at a time, following the proper dependency order:

diff --git a/docs/faq.md b/docs/faq.md
@@ -107,6 +107,12 @@ The high-level migration path is:
 - **Domain Admin** membership is required for full deployment
 - Scoped deployments (e.g., `-OuAclsOnly`) may work with delegated permissions — to be confirmed per use case
 
+### What language or locale is supported?
+- **English (`en-US`) only, at this time.** Both the **host** you run the scripts from (your workstation or the domain controller) and **Active Directory** must be English.
+- The tool runs **two fail-fast prerequisite checks** — one for the host OS install language, one for the well-known Active Directory group names — and stops with a clear message on a non-English environment **before making any change**.
+- Only 18 languages fully localize Windows Server (including AD group names); English is supported and the other 17 are detected and stopped. Language Interface Packs (e.g. Hindi, Bengali) and non-bold language packs (e.g. Arabic) keep English AD names and are unaffected.
+- See [Language Support](language-support.md) for the full language list and the future localization roadmap.
+
 ### What PowerShell modules must be installed?
 - `ActiveDirectory` (v1.0.1.0 or later)
 - `GroupPolicy` (v1.0 or later)
@@ -324,6 +330,7 @@ The time and energy spent trying to minimize the Tier Model footprint would be f
 - Confirm you are running as Domain Admin
 - Confirm network connectivity to the `-PreferredDc` specified
 - Check that all required modules are installed at the correct versions
+- Confirm the **host OS** (where you run the scripts) and **Active Directory** are English (`en-US`) — non-English environments are not supported (see [Language Support](language-support.md))
 
 ### An OU was not created. Why?
 - The OU may already exist (check the log for "OU already exists" INFO messages)

diff --git a/docs/index.md b/docs/index.md
@@ -29,3 +29,7 @@ Welcome to the Active Directory Tier Model documentation.
 - **[Test Tag Matrix](test-tag-matrix.md)** - Test organization, tagging, and execution strategies
 - **[Test Coverage](test-coverage.md)** - Comprehensive test coverage analysis and roadmap
 - **[CI/CD Integration](ci-cd.md)** - Continuous Integration and Deployment pipelines
+
+## Reference
+
+- **[Language Support](language-support.md)** - Supported languages (English only today), the 18 fully-localized Windows Server languages, and the roadmap and challenges for community localization