About the Domain Feature, Shopify recently added a new feature for Domains, so the old way to activate the Domain Feature won't work anymore, for certain stores.
However, I can now show you the steps to make this work, by following the new Shopify Markets process.
The first thing to do would be going to shopify > settings > markets:
From there, you will have to click on add market on top:
In the following window you would have to pick the region you want to address this language to:
Then in the following screen, you would have to setup all the options about this Market, including the subdomain for the language:
After that, the Market will be active and the language should be correctly associated with it.
I hope this helps. Please, feel free to reach out back to us if you need any additional assistance.