Internet connection is not required in iOS 13+ if the language data is available on the device.
It should happen automatically.
You can test whether it is available offline with:
'based on the example code
If speech.SetLanguage(lang) = False Then
TextView1.Text = "Speech Recognition not available."
Else
TextView1.Text = "Ready!"
If App.OSVersion >= 13 Then
Dim no As NativeObject = speech
Dim OfflineSupported As Boolean = no.GetField("recognizer").GetField("supportsOnDeviceRecognition").AsBoolean
Log(OfflineSupported)
End If
SetState(True)
End If