Add your garmindevice.xml on PC for backup
Open garmindevice.xml on your nuvi with notepad and hit ctr+F and write voice and hit enter ( for next search you pres button F3)
Search for something like this: PartNumber>006-D0397-00</PartNumber><Version><Major>2</Major><Minor>20</Minor></Version><Path>Garmin/Voice</Path><FileName>English_American_.vpm

Now edit <Version><Major>2</Major><Minor>20</Minor> to <Version><Major>1</Major><Minor>20</Minor>

Do this for all voice you like to download and then save

Run webupdater and you can now download voice for your nuvi