you have to add the webview to a parent view like the activity:
B4X:
Sub Activity_Create(FirstTime As Boolean)
'Do not forget to load the layout file created with the visual designer. For example:
'Activity.LoadLayout("Layout1")
Dim WebView1 As WebView
WebView1.initialize("xxx")
Activity.AddView(WebView1,0,0,100%x,100%y)
WebView1.LoadUrl("http://translate.google.com/translate_tts?tl=de&q=Edel")
End Sub