A Twitter 'Web Intent' link generator that allows for merge tags to be left in for use with Mailchimp, after encoding the URL. Web intent is Twitter's name for a link that autopopulates a tweet for the user when clicked on.
A Tweet Web Intent makes it easy for your site visitors to compose and post a Tweet to their audience from a link on your webpage. Sites may configure Tweet text and hashtags, pass a URL, and identify Twitter accounts related to the page.