Public/Configuration/Set-MailboxDefaultLanguage.ps1

function Set-MailboxDefaultLanguage {
    param(
        [Parameter(Mandatory)]
        [string]$TenantId
    )

    try {
        Write-ModuleLog -Message "Setting default language for tenant $TenantId" -Level Info -Component 'Set-MailboxDefaultLanguage'
        Connect-CustomerExchange -CustomerTenantId $TenantId

        get-exomailbox | Where-Object Name -NotLike 'Discovery*' | ForEach-Object {
            $mail = $_.UserPrincipalName
            $lang = (Get-MailboxRegionalConfiguration -Identity $mail).Language
            if ( $lang -ne 'da-DK' ) {
                Write-ModuleLog -Message "Changing language to danish for $mail" -Level Info -Component 'Set-MailboxDefaultLanguage'
                Set-MailboxRegionalConfiguration -Identity $mail -Language da-DK -DateFormat "dd-MM-yyyy" -TimeFormat "HH:mm" -LocalizeDefaultFolderName -TimeZone "Romance Standard Time"
            }
        }
    }
    catch {
        throw $_
    }
}