Konstantin Obenland

This plugin needs Jetpack by WordPress.com to be activated and its Sharing module to be enabled. 
Enter the desired Twitter usernamen in Settings -> Sharing. It will then be appended, every time a visitor shares your content on Twitter
See the <a href="https://dev.twitter.com/docs/tweet-button" title="Tweet Button" rel="nofollow ugc">Tweet Button documentation</a> for details.
<h4>Translations</h4>
I will be more than happy to update the plugin with new locales, as soon as I receive them! 
Currently available in:
<ul>
<li>English</li>
</ul>

Jetpack Twitter Via

Adds 'via @username' to the Tweet Button provided in "Jetpack by WordPress.com"

Dominik Schilling

required

This plugin helps you to declutter your WordPress admin by removing all Jetpack related notices that promote services like the backup services VaultPress, WordPress Apps or Blaze.

Jetpack Without Promotions

WordPress dashboard is a stage for abusive use of screen estate. The fact that Jetpack, a plugin by the company that confuses itself with WordPress, is leading the way in this abusive use is just wrong, a shame really, and setting the wrong example for all plugin and theme authors.

WordPress urgently needs a way to put this nags where they belong: the plugin/theme specific settings page or some kind of notification center.

Thank you Required for helping to clean up. It is not a definitive solution but it is a welcome panacea.

The plugin that should not be

Removes all admin notices for promotions added by Jetpack.

Jetpack Twitter Via vs Jetpack Without Promotions