Lua is a programming language, a fairly high level "scripting" one. Various emulators, though most notably FCEUX for the NES and Desumume for the DS, added the ability to run Lua scripts on top of games and speak to the games in a way that ROM hackers would find useful (the game's memory addresses, registers....). Being a programming language run on the PC though you can then quite happily pass commands on to other programs/scripts/whatever. From there you can pass on command line commands or something to a program like http://espeak.sourceforge.net/
and have what you want. If there are few enough snippets then you might even be able to convince someone to narrate the lot and then call the resulting sound files.
Here is a discussion on a lua hack for a NES game we had recentlyhttp://www.romhacking.net/forum/index.php/topic,18717.0.html
The sorts of changes it could make would be hard to do if you kept to the limits of hardware. Some of the tool assisted speedrunning people also make fairly extensive use of these scripts and similar ones that you could find useful.
If none of the N64 emulators ever got Lua, I genuinely do not know at this point, and the DS versions of pokemon are not what you want then you can make things slightly harder, but still far short of having to effectively make a speech synthesis engine in the equivalent of the N64's hardware (which is what an emulator is simulating after all). The way I would set about it would be to look at the cheat making tools -- not every emulator has good cheat making support but the general theory of cheat making is quite easy (you search the memory/watch things in memory and act accordingly), to this end tools have been made that attach to emulators to allow them to have cheats made even if the emulator itself does not have proper cheat searching. What one is the most popular seems to vary depending upon where you are in the world and what console/device/game series you are hacking. emuhaste and artmoney are probably the most well known of the current set, emuhaste is even open source. As all the Lua script would be doing is reading the appropriate points in the game's memory and calling things accordingly and a cheat making tool is designed to read things in the game's memory and do some action...
We have had a few hard of sight (you probably only need to go a few pages back in this very topic for that one), hearing or motor control ability use various similar techniques to help them play games they would otherwise struggle to. I can not say I have seen stuff for fully blind people but the theory of operation is no different to those things already covered.
It will mean you need a PC rather than a flash cart but controller adapters are easy to come by and, if you will permit a joke potentially in poor taste, it is not like the visual fidelity issues that many would be proponents of real hardware seem to latch onto are going to be especially troublesome in this case.