Refactor the warning messages for discouraged languages

The warning for discouraged languages was very long and included HTML.
Previously it had wiki markup, which required using parsing through API.
The change to HTML resulted in incorrectly escaped <strong> tags
because of parsing on both client and server.

This commit splits these message into two shorter messages each,
removes the HTML and makes some more fixes in the code around them.

Change-Id: I17c1cb0190ef26db3bf9e1c42a3a0ccdad290f0b