#Requires -RunAsAdministrator
<#
Sets Windows language on Windows 10/11.

Menu:
1 = English (en-US)
2 = Svenska (sv-SE)
3 = Norsk Bokmal (nb-NO)

Modes:
- Quick = Current user display language, language list, keyboard, culture, and home location
- All   = Quick settings plus system preferred UI language, system locale, and defaults for system/new users

Notes:
- Requires Administrator.
- Requires internet access to Windows Update, or a configured FoD/WSUS source.
- Restart or sign out/sign in is required before the Windows shell fully changes language.
- If this is run as SYSTEM, HKCU means the SYSTEM profile, not the signed-in user.
- Avoids collection method calls so it can run more reliably under Constrained Language Mode.
#>

param(
    [string]$Choice,
    [string]$Mode
)

$ErrorActionPreference = "Stop"

function Write-Section {
    param(
        [string]$Title
    )

    Write-Host ""
    Write-Host "== $Title =="
}

function Write-Step {
    param(
        [string]$Message
    )

    Write-Host (" - {0}" -f $Message)
}

function Write-WarningStep {
    param(
        [string]$Message
    )

    Write-Host (" ! {0}" -f $Message)
}

function Get-FirstLanguageTag {
    param(
        $LanguageList
    )

    foreach ($language in $LanguageList) {
        return $language.LanguageTag
    }

    return $null
}

function Test-CommandExists {
    param(
        [string]$Name
    )

    $command = Get-Command -Name $Name -ErrorAction SilentlyContinue

    if ($null -eq $command) {
        return $false
    }

    return $true
}

function Install-LanguageWithLanguagePackManagement {
    param(
        [string]$Tag,
        [string]$SelectedMode
    )

    if (-not (Test-CommandExists -Name "Install-Language")) {
        return $false
    }

    Write-Step "Using LanguagePackManagement Install-Language for $Tag"

    if ($SelectedMode -eq "All") {
        Install-Language -Language $Tag -CopyToSettings | Out-Null
    }
    else {
        Install-Language -Language $Tag | Out-Null
    }

    return $true
}

function Install-LanguageWithWindowsCapability {
    param(
        [string]$Tag,
        [string]$SelectedMode
    )

    if (-not (Test-CommandExists -Name "Get-WindowsCapability")) {
        throw "Neither Install-Language nor Get-WindowsCapability is available on this system."
    }

    if ($SelectedMode -eq "Quick") {
        $capabilityPrefixes = @(
            "Language.Basic"
        )
    }
    else {
        $capabilityPrefixes = @(
            "Language.Basic",
            "Language.OCR",
            "Language.Speech",
            "Language.TextToSpeech",
            "Language.Handwriting"
        )
    }

    Write-Step "Using Windows capabilities fallback for $Tag"

    $allCaps = Get-WindowsCapability -Online

    foreach ($prefix in $capabilityPrefixes) {
        $caps = $allCaps | Where-Object { $_.Name -like "$prefix*~~~$Tag~*" }

        if (-not $caps) {
            Write-Step "${prefix}: not available for $Tag on this system, skipping"
            continue
        }

        foreach ($cap in $caps) {
            if ($cap.State -eq "Installed") {
                Write-Step "$($cap.Name): already installed"
            }
            else {
                Write-Step "Installing $($cap.Name)"
                Add-WindowsCapability -Online -Name $cap.Name | Out-Null
            }
        }
    }
}

function Set-CurrentUserLanguage {
    param(
        [string]$Tag,
        [string]$InputTip,
        [int]$GeoId
    )

    $currentList = Get-WinUserLanguageList
    $newList = New-WinUserLanguageList -Language $Tag

    foreach ($item in $currentList) {
        if ($item.LanguageTag -ne $Tag) {
            $newList += $item
        }
    }

    Set-WinUserLanguageList -LanguageList $newList -Force | Out-Null
    Set-WinUILanguageOverride -Language $Tag
    Set-Culture -CultureInfo $Tag
    Set-WinHomeLocation -GeoId $GeoId
    Set-WinCultureFromLanguageListOptOut -OptOut $False
    Set-WinAcceptLanguageFromLanguageListOptOut -OptOut $False

    if ($InputTip) {
        Set-WinDefaultInputMethodOverride -InputTip $InputTip
    }
}

function Set-ComputerWideLanguage {
    param(
        [string]$Tag
    )

    Set-WinSystemLocale -SystemLocale $Tag

    if (Test-CommandExists -Name "Set-SystemPreferredUILanguage") {
        Set-SystemPreferredUILanguage -Language $Tag
    }
    else {
        Write-WarningStep "Set-SystemPreferredUILanguage is not available; system preferred UI language was not changed"
    }

    Copy-UserInternationalSettingsToSystem -WelcomeScreen $True -NewUser $True
}

function Test-LanguageResult {
    param(
        [string]$Tag,
        [string]$SelectedMode
    )

    $problems = 0

    Write-Section "Verification before restart"

    $verifyList = Get-WinUserLanguageList
    $primaryLanguage = Get-FirstLanguageTag -LanguageList $verifyList

    if ($primaryLanguage -eq $Tag) {
        Write-Step "Primary user language is $Tag"
    }
    else {
        Write-WarningStep "Primary user language is $primaryLanguage, expected $Tag"
        $problems = $problems + 1
    }

    $uiOverride = Get-WinUILanguageOverride

    if ($null -ne $uiOverride -and $uiOverride.Name -eq $Tag) {
        Write-Step "User UI language override is $Tag"
    }
    else {
        Write-WarningStep "User UI language override is not $Tag"
        $problems = $problems + 1
    }

    $culture = Get-Culture

    if ($culture.Name -eq $Tag) {
        Write-Step "User culture is $Tag"
    }
    else {
        Write-WarningStep "User culture is $($culture.Name), expected $Tag"
        $problems = $problems + 1
    }

    if ($SelectedMode -eq "All") {
        $systemLocale = Get-WinSystemLocale

        if ($systemLocale.Name -eq $Tag) {
            Write-Step "System locale is $Tag"
        }
        else {
            Write-WarningStep "System locale is $($systemLocale.Name), expected $Tag"
            $problems = $problems + 1
        }

        if (Test-CommandExists -Name "Get-SystemPreferredUILanguage") {
            $systemPreferred = Get-SystemPreferredUILanguage

            if ($systemPreferred -eq $Tag) {
                Write-Step "System preferred UI language is $Tag"
            }
            else {
                Write-WarningStep "System preferred UI language is $systemPreferred, expected $Tag"
                $problems = $problems + 1
            }
        }
    }

    return $problems
}

if (-not $Choice) {
    Write-Host ""
    Write-Host "Choose language:"
    Write-Host "1 = English"
    Write-Host "2 = Svenska"
    Write-Host "3 = Norsk Bokmal"
    Write-Host ""

    $Choice = Read-Host "Enter 1, 2, or 3"
}

switch ($Choice) {
    '1' {
        $LanguageTag  = 'en-US'
        $LanguageName = 'English (United States)'
        $InputTip     = '0409:00000409'
        $GeoId        = 244
    }
    '2' {
        $LanguageTag  = 'sv-SE'
        $LanguageName = 'Svenska (Sverige)'
        $InputTip     = '041D:0000041D'
        $GeoId        = 221
    }
    '3' {
        $LanguageTag  = 'nb-NO'
        $LanguageName = 'Norsk Bokmal (Norge)'
        $InputTip     = '0414:00000414'
        $GeoId        = 177
    }
    default {
        Write-Host "Invalid choice: $Choice"
        Write-Host "Use 1, 2, or 3."
        exit 1
    }
}

if (-not $Mode) {
    Write-Host ""
    Write-Host "Choose mode:"
    Write-Host "1 = Quick (current user language/display settings)"
    Write-Host "2 = All (current user + system-wide settings)"
    Write-Host ""

    $modeChoice = Read-Host "Enter 1 or 2"

    switch ($modeChoice) {
        '1' {
            $Mode = "Quick"
        }
        '2' {
            $Mode = "All"
        }
        default {
            Write-Host "Invalid mode: $modeChoice"
            Write-Host "Use 1 or 2."
            exit 1
        }
    }
}
else {
    switch ($Mode) {
        'Quick' {
            $Mode = "Quick"
        }
        'All' {
            $Mode = "All"
        }
        'quick' {
            $Mode = "Quick"
        }
        'all' {
            $Mode = "All"
        }
        default {
            Write-Host "Invalid mode: $Mode"
            Write-Host "Use Quick or All."
            exit 1
        }
    }
}

Write-Host ""
Write-Host "Selected language: $LanguageName [$LanguageTag]"
Write-Host "Selected mode: $Mode"

Write-Section "Execution context"
$currentIdentity = whoami.exe
Write-Step "User: $currentIdentity"
Write-Step "PowerShell language mode: $($ExecutionContext.SessionState.LanguageMode)"

if ($currentIdentity -eq "nt authority\system") {
    Write-WarningStep "Running as SYSTEM. Current-user settings will apply to SYSTEM, not the signed-in user's HKCU profile."
}

Write-Section "Installing language"

$installedWithLanguagePackManagement = $false

try {
    $installedWithLanguagePackManagement = Install-LanguageWithLanguagePackManagement -Tag $LanguageTag -SelectedMode $Mode
}
catch {
    Write-WarningStep "Install-Language failed: $($_.Exception.Message)"
    Write-WarningStep "Trying Windows capability fallback"
}

if (-not $installedWithLanguagePackManagement) {
    Install-LanguageWithWindowsCapability -Tag $LanguageTag -SelectedMode $Mode
}

Write-Section "Configuring current user"
Set-CurrentUserLanguage -Tag $LanguageTag -InputTip $InputTip -GeoId $GeoId
Write-Step "User language list, UI override, culture, home location, and default keyboard set"

if ($Mode -eq "All") {
    Write-Section "Configuring computer-wide settings"
    Set-ComputerWideLanguage -Tag $LanguageTag
    Write-Step "System locale, system preferred UI language, and default account settings applied where supported"
}
else {
    Write-Section "Skipping computer-wide settings in Quick mode"
    Write-Step "System locale not changed"
    Write-Step "System preferred UI language not changed"
    Write-Step "Welcome screen and new user defaults not changed"
}

$problemCount = Test-LanguageResult -Tag $LanguageTag -SelectedMode $Mode

Write-Host ""

if ($problemCount -gt 0) {
    Write-Host "Completed with $problemCount verification warning(s)."
    Write-Host "If these warnings show the old language immediately after running, a policy, missing language pack, or wrong execution account is preventing the change."
    exit 2
}

Write-Host "Done."

if ($Mode -eq "All") {
    Write-Host "Language set to $LanguageName [$LanguageTag] for the current user and computer-wide defaults."
}
else {
    Write-Host "Language set to $LanguageName [$LanguageTag] for the current user."
}

Write-Host "Restart the computer, or sign out and back in, to fully apply the Windows UI language."