I've tried this code on Nexus 5 and it worked correctly:
B4X:
Sub Activity_Click
mp.Initialize("mp")
Dim su As StringUtils
mp.Load("http://translate.google.com/translate_tts?tl=th&q=" & su.EncodeUrl("ทู", "utf8"))
End Sub
Sub mp_StreamReady
Log("Ready")
mp.Play
End Sub