Create Managed Metadata Property and Mapping
$searchAppName="Enterprise Search Service Application"
$searchapp = Get-SPEnterpriseSearchServiceApplication $searchAppName
$category = Get-SPEnterpriseSearchMetadataCategory –Identity SharePoint -SearchApplication $searchapp
#Creating Metadata properties
$CrawlPropertyName="ows_Avanade-GBP-PageLanguage"
$managedPropertyName="PageLanguageFromPS"
$crawledproperty = New-SPEnterpriseSearchMetadataCrawledProperty -SearchApplication $searchapp -Category "Sharepoint" -VariantType 31 -PropSet "00130329-0000-0130-c000-000000131346" -Name $CrawlPropertyName -IsNameEnum $false
$managedproperty = New-SPEnterpriseSearchMetadataManagedProperty -SearchApplication $searchapp -Name $managedPropertyName -Type 1
New-SPEnterpriseSearchMetadataMapping -SearchApplication $searchapp -ManagedProperty $managedproperty -CrawledProperty $crawledproperty