Welcome!
First, if you have a question about how to do something with the library, join #elm-ui on the Elm Slack! There are usually a number of people who are willing to help out, myself included.
That's the place to ask questions, try there first.
A few notes about my design process for elm-ui.
I don't usually accept PRs that add features. Mainly this is because there is a bunch of design thought and research that needs to be done before a feature can be added.
So, here are some other ways you can help if you so desire!
If you run into unexpected behavior, I definitely want to hear about it. Put together a Short, Self Contained, Correct, Example of what you're encountering. It really helps if the example is as succinct as possible.
Here's a basic template in ellie to get you started!
One of the more challenging parts of the project like this is gathering information.
If you know of good resources about accessibility, internationalization, design, or any of the topics listed in the research folder, send them my way either via PR to those documents or on slack.