I think this is getting silly.
I have first hand experience with how these things get out of hand, and you can see it starting to happen right now. If you allow something like "synonyms", you're going to get people voting in other languages, some of which the Speaker may understand and some of which they may not, but which can lead to discrimination in which get counted and which get discounted. You're going to get people posting in emojis, then arguing over whether :silly: is
obviously a vote for (it's smiling!) or
obviously a vote against (an upside-down smile is a frown!). You're going to get people posting GIFs, then others complaining that when those links are inevitably lost we won't have a record of how that person voted.
As for trying to create an exhaustive list? Well, that has its own dangers. Suppose we use Amerion's draft:
"Aye", "Approve", "Yes", "Acceptable", "Affirmative", "In Favour", or "For" to vote in the affirmative
Well, now you're gonna get arguments. If all those, why not "sure"? Why not "yeah"? Why not "okay" or "super" or "excellent" or "heck yeah" or "goodness yes" or "your ideas intrigue me and I would like to subscribe to your newsletter" or "shut up and take my money!"? Why not "ja", I mean, we all know that one after all, it's not like it's crazy arabic. But for that matter, why
not crazy arabic, since if we're making a firm list we can just put the romanization *and* the arabic letters in there and it's fine. And why not elvish and klingon while we're at it? And maybe we could also include emojis in the list?
and
are pretty straightforward after all, everyone knows what those mean.
I'm being humerous but I'm not actually kidding. These are all things I have personally seen happen when a speaker of an assembly tries to open things up to some flexibility. People love to push the boundaries of what's allowed and what isn't, and I can't even say that I myself am above doing that. Sometimes we all have a rebellious FU to authority that's trying to get out.
Pick ONE thing. Yes/No/Pass, Aye/Nay/Abstain, For/Against/Present. Not all three. Not two. ONE thing. It is not onerous or an impediment to someone's right to vote to require that they use that one thing to cast their vote, without embellishment. It is the simplest and best solution that avoids any messy kerfuffles over exactly what is allowed.
I have no strong preferences between the options; any would be fine. But...
only one.