Best to avoid express if you can. If you can use WebUpdater for firmware as said above and it's ok for voice files etc, and use MapUpdater for new maps [if you have Lifetime Maps or buy them].
About the dictionary, i don't really know if the voice translation will work ok for sure with SG fw, need to mod the firmware for additional voices such as ES to know that. But the written EN-ES translation works on screen for me with SG, the voice can't work because i only have working EN voices on-board at present, it has the speaker icon for ES but won't play because the ES voice OB isn't in the SG fw yet. Baby steps, let's just get SG fw on your 765 and then we'll worry about the next step [i'm actually hoping i can get you to do the voice mod for the fw too - give a man a fish etc .... otherwise i'll want a pallet of beer ].