Greek caught my attention 
If you’re on Windows, take a look at this thread
There’s a code snippet there that allows you access to the Windows system languages.
Then your problem becomes installing a Greek language voice. They’re referred to as “Legacy Voices”
It seems that there is a male Greek voice (Stefanos) supported, but I wasn’t able to make use of it. Maybe it has to do with my edition of Windows and you’ll have better luck.
But accessing system voices via an OLE object no longer keeps you tied to whatever is behind System.Speak of the Xojo framework.
Good luck with it 
-edit- just noticed that you’ve mentioned Safari, so you’re probably on a Mac