Now your Template:USERNAME is working. Isn't that what you needed?
You didn't, you copied Dev: instead of dev:. Decapitalize the first letter in there.
You'll need to edit MediaWiki:ImportJS on that wiki to add the following line:
What is your issue and what is your wiki?
That envelope icon is for notifications from threads (Forum or Message Wall). Threads no longer exist on UCP in any form and so that icon will be removed.
I don't see any mailbox on my profile on this wiki nor on UCP wikis. Do you have a link or a screenshot of what you're talking about?
What mailbox thingy?
There is no announced date yet.
You click on the link provided in the step and then depending on your operative system (as mentioned in the dotpoints below the first step) click on the link on the releases page for your operative system.
We don't have any official information about that. We don't have any official information about whether Chat will actually be ported to the UCP, either.
Not yet, no.
What step in the documentation are you stuck on?
Yes, you can. It is documented in the step 3 and step 4 of the installation instructions.
Why wouldn't the data-sort-value attribute help there? I created an example in my sandbox here with how data-sort-value would work with your infinite values, and it sorts the table properly while not displaying extraneous data on the mobile skin.
There isn't, and there probably shouldn't be, as displaying different content across different devices hurts the SEO of your wiki. Sortable tables have a data-sort-value attribute for every row that you can use, which doesn't require the value to be inside of table content and therefore will be hidden on mobile.
The Help page for Discussions states: "A few select communities offer the option of creating a quiz, but this is a beta feature that's not available everywhere." Presumably, the feature will be available to all communities at some point.
I unbroke your settings page now and it's appearing on your test account's userpage for me. Please always use the Medals interface to set up medals instead of editing that page directly.