People familiar with the matter report that individual voices range from about a third to more than a half gigabyte each, and that Apple will supply the voices as downloadable options that can be selectively installed by the user.
The 53 new voices are not yet available for download from Apple, but a synthesized demo of each voice can be played as a demo.
In addition to Leopard's current Alex voice from 2007 and the Vicki voice added to Mac OS X Panther in 2003 (and several previous, but fairly robotic-sounding speaking and novelty voices that have shipped on Macs since the late 80s), Lion will make available three new very high quality American English voices: Tom, Samantha and Jill.
Additionally, Lion adds new regional English variants, including an Australian English Karen and Lee; British English Daniel, Emily and Serena; Scottish English Fiona; Indian English Sangeetal; Irish English Moira and South African English Tessa.
Apple will also include other language voices for the first time, including Saudi Arabian Arabic Maged; Chinese voices representing a Mainland China Ting-Ting, Hong Kong Sin-Ji, and Taiwan Ya-Ling; Czech Zuzana; Danish Ida; Belgian Dutch Ellen; Netherlands Dutch Claire and Xander; Finnish Mikko; French Canadian Felix and Julie; French Sebastien, Thomas and Virginie; German Anna, Steffi and Yannick; Greek Alexandros; Hindi Lekha; Hungarian Eszter; Indonesian Damayanti; Italian Paolo and Silvia; Japanese Kyoko; Korean Narae; Norwegian Stine; Polish Agata; Brazilian Portugese Raquel; Portugese Joana; Romanian Simona; Russian Milena; Slovak Laura; Mexican Spanish Javier and Paulina; Spanish Diego and Monica; Swedish Alva and Oskar; Thai Narisa; and Turkish Aylin.