Hm, yes, I think this already done and an example is somewhere out in the web.
Let me search for it…
Ah, yes here it is, two scripts by Martin Fischer at hilfdirselbst.ch :
The first one is working as is on selected text, the second one is designed as a context menue and the script should be put in your "startup scripts" folder. Don't know, but perhaps there is a problem, if you are doing the search with special characters on a Windows machine.
Hm. Just tested the code and it is not working anymore. Maybe it should adapted to a newer version of InDesign. Also it seems that request should be changed for https and an international version of Google.
Tested with InDesign CS5.5 on Mac OSX 10.6.8 (German) with Firefox 34.0.5 German.
Ah. It's working somehow.
But I guess for single words only. No whitespace in the selected text aloud.
Test for yourself…