I've been using wee_slack.py for some time; if you can add an application token and prefer the weechat UI then it's an appreciable option, but the issues I've had regarding inputting code are not necessarily fixed there since weechat doesn't take multi-line input. :(
Whoops, sorry about that. I'll have to double check I was 90% that was standard in weechat or wee-slack - I've installed very few non-standard plug-ins.