Microsoft Speech Synthesis, SpeakSsmlAsync with out lang attribute

Question

I am using Microsoft Speech Synthesis to play my SSML string using public Prompt SpeakSsmlAsync(string ssmlText); and i got a requirement where i should not use xml:langbut when i remove xml:lang attribute from the ssml string i am getting below exception

'speak' requires attribute 'xml:lang'

So is there a way that i can play my SSML string without using xml:lang attribute and let speech engine handle it ?

What i want to play but fails :

<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis">
  helloo
</speak>

Working one with lang attribute:

<speak version="1.0" xmlns="http://www.w3.org/2001/10/synthesis" xm:lang="en-US">
  helloo
</speak>

Thanks in advance.