It sounds as if you're starting with English text but your voicebox will be expecting a sequence of phonemes, so you'll need something clever to work out how to pronounce each word. the Sparkfun tutorial just has a few words hard-coded in a local dictionary but that is a very limited solution. To do the conversion in a way that can cope with arbitrary words is going to be tricky, and the TTS256 you linked to seems like the sort of thing you need to do it. You mention Google Translate at the beginning. Is this box intended to do language translation too?
Have you found any examples showing how to connect a PS/2 keyboard to an Arduino? I guess that's using some sort of serial interface but I don't know any details about it. It might be easy to interface to, but if not then I remember seeing a USB hosting shield so I guess plugging a USB keyboard in would be straight forward. I don't know how the keyboard output is encoded over the USB, you will probably need a scancode-to-character conversion, but that is quite feasible.
Alternatively, you may find some kind person has already designed a keyboard that can interface to an Arduino directly.
I think mayb i will try make this device to stick for English word only..
but in this video had show TTS256 need to interface with using a X-CTU to write the text..
is it possible if this TTS256 can run directly that means if we write it directly using keyboard and it will appear at the LCD and when press "ENTER" it will pronounce the word?.
this show how to use a PS2 keyboard by using the PS2 keyboard library