Multilingual network

I have installed the network and it’s working wonderfully at https://thecentralohionetwork.com (all of the posts there are dummy posts/blogs so far).

However, I’ve also installed the Sorani Kurdish language files and while the administration backend is in Kurdish, there are a few pages along the way that aren’t translated at all. The registration page, for example.

I have two questions… the first obviously being how do I fix that?

The second: I would like for users to choose their language when they first get to the site – so they can choose to read, register, administer the entire site (front end and back) in either English, Kurdish (and perhaps others).

How can I make that happen? The site is for a Kurdish population, but they have multiple dialects (both available already in WP translations), but readers might like to read/contribute in either Kurdish or English.

Any thoughts?