which are typically saved in ASCII
GCC defaults to UTF-8, using that it's actually not that much of an issue. However, the algorithms used to work with the affected strings need to be able to support UTF-8 to some degree as well.
I'm not really thinking about the compiler, I am more thinking about the editor and source control. Some default to ASCII, most support UTF-8 if asked, however some don't support UTF-8 at all. And yes, definitely the algorithms need to support UTF8, and the UTF8 characters need to be available at runtime, and so on..
Yes, for various reasons we certainly do need button names that can be expressed in plain ASCII. The question is: do they need to be single character names like A B C, or is it OK if the ASCII rendering of their name takes multiple characters like START, SELECT, PYRA, DELTA, PI, OMEGA, CHI ?
If single character names are a must, then A B C X Y Z or A B C D X Y are the only options; we can't use numbers because that would be confusing, we can't use ASCII symbols like + * # because that would also be confusing. The main problem I see with using normal letters is that there is probably not going to be any sane way to keep the 4 Pandora buttons like they are and add 2 extra buttons to that. It depends on where the extra buttons would be, but e.g. something like this:
Z
Y C
A B
X
or something like this:
Z Y
A B
C X
looks really, really weird to me. Also, every console controller seems to have a different way to label ABXY, so for emulation it's kind of confusing to have to remember things like "If the game says A, then I have to press X; if it says B I have to press A; if it says Y I have to press B etc etc", and for another system it's different again. For me such things are easier to remember if two different symbol sets are used.
Something like this:
Σ
Δ Ψ
Π Ω
X
would look quite cool imo. The X is the only one that looks the same on Pyra and Pandora, but that's enough to find your way if you're used to the Pandora way. For Playstation emulation (including PSP), these symbols are quite good because Pi and Omega are "close enough" to box and circle. For emulation of consoles that use ABXY, it's hopeless anyway, but at least it's less confusing if the buttons have different symbols than if they have the same symbols in a different order.