> Slack provides an IRC bridge that lets you connect to Slack with an IRC client.
Which doesn't exist anymore: https://news.ycombinator.com/item?id=16539857. As far as I'm aware, there is no way to connect to Slack anymore without their official client, unless you use something that is either their website in an app wrapper or probably violating their ToS.
weechat has a plugin called wee-slack that I've been using every day for over a year https://github.com/wee-slack/wee-slack