Answer to: How Far Would You Go to Accommodate non-Verbal Colleague?

"Drawing the line" already indicates you probably have the wrong mindset here. It's clear that your colleague is perfectly capable of performing his work and undermining his productivity and morale in seeking ways to bypass him seems (at least to me) to be wrong. The simplest and most effective solution is to work with him as a remote worker, so that work related requests are conducted via Slack/e-mail/whatever. This should really be the case as you'd want an audit trail anyway. Additionally, you might want to look at positive ways in which you can interact - you don't have to learn sign language, a few simple changes would go a long way toward including your colleague and letting him feel as though he's a part of the team. YouTube has a ton of resources. Also watch other people in your team (and talk to them) and learn how they interact.