brushup admin interface

Hi, Taggic. I recently installed the LangDelete plugin and find that it is much helpful to keep reduced files under our daily backup. The current version of the plugin worked fine with the most recent DokuWiki 2014-05-05 "Ponder Stibbons".

I think that there is something I can do to improve the plugin:

* use DokuWiki's msg() function to display any message, to accommodate better with dokuwiki template
* rework Input form design, to emphasize that admin must specify Lang-code that he want to keep, not delete
* separate longer text in lang.php to text file for easing translation to other languages.

It is glad if you like my work for the plugin, even I could not complete german language files.