Admin in English lets you have your administration panel in English, even if the rest of your blog is translated into another language.
The plugin just does what it says : after installing it, you can just forget about it. ;)
There would be only one thing to change. As mentioned by some other users before, the plugin is forcing the wp-login.php in English as well. If you have a community oriented website with members, the login page is definitely part of the front end.
dainius.kaupaitis posted a snippet to solve this problem here : wordpress.org/support/topic/login-page-is-forced-to-english-too
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