Hi @Echo Du_MSFT Thanks for your reply.
I already activated this feature and getting "Enable pages and news to be translated into multiple languages"
option.
I wanted to set it on( slide the toggle to On) by pnp code and add alternative language.
Was able to do it, we need to activate one more feature "MultilingualPages"
enable MultilingualPages feature
Enable-PnPFeature -Identity 24611c05-ee19-45da-955f-6602264abaf8
$Web = Get-PnPWeb -Includes RegionalSettings.InstalledLanguages
$Web.RegionalSettings.InstalledLanguages
$Web.IsMultilingual = $true
$Web.AddSupportedUILanguage(1036)
$Web.Update()
Invoke-PnPQuery