If you really want to keep this issue going you should talk to a lawyer, but just for what it's worth (I'm not a lawyer) them "knowing" probably doesn't matter as much as whether or not you asked for specific accommodations for your communications problems, disclosing to them the medical reason for asking for them.
There's a lot of reasons to think this is a long-shot:
(a) You're non-US and abroad, so the ADA doesn't apply to you
(b) You're probably a contractor and not an employee
(c) Even if it applies, the ADA doesn't make it unlawful to fire you for poor performance
I think it's worth talking to a pro about this, but it's not worth spending a lot of money pursuing it, mostly because of (a). If you were a US resident, I'd say (b) and (c) are hurdles low enough that you could plausibly shake a settlement loose, but (a) is a very high hurdle.
