Peter Lawrenson

The plugin enables the easy deletion of unwanted translations. This will remove nags to update translations for unwanted locales, and enable some server disk space to be reclaimed. Website back-ups will be a bit quicker and backup files will be a bit smaller.
Deletion of unwanted translations can be done using FTP and the site host’s file manager, or by using a file manager plugin, but administrators should find this easier and quicker with this plugin. The plugin will suit administrators who are uncomfortable with using FTP or who don’t have FTP access.
<h3>Deactivating</h3>
Deactivate or delete the plugin at Dashboard > Plugins > Installed Plugins
<h3>Usage</h3>
Go to Dashboard > Tools > Translation Remover
Select the translations you would like to be removed. Several can be removed with one pass.
The default action is to just list the translation files so you can check they are the correct ones, or you can select the deletion of the files.
Click “Go”.
The plugin will not allow the removal of translations for the active locale. To remove the translations for the active locale, go to Dashboard > Settings > General and select a new site language. When you come back to the Translations Removal tool, the original site language translations can be selected for removal.
If you inadvertently remove any translations that you would like to keep, select their locale as the site language, go to Dashboard > Updates and click the “Update translations” button.
The locale: “English (United States)” is the language used in the code. It doesn’t have any translation files.

Simple Translation Remover


Simple, easy, perfect.



I've tried with some test webs and it worked fine. It does what is expected.


It does what it promises

unclego

Lets you have your backend administration panel in english or any installed language, even if the rest of your blog is translated into another language. Language preferences can be set per user basis in user profile screen.
Tested on MultiSite.
Deals with frontend ajax requests
Notice: 
After release of WordPress 4.7 this plugin is a bit obsolete.
In WordPress 4.7 users are able to select their preferred locale (language) when editing their profile. Plugin add exact same functionality to pre 4.7 WordPress.
I still maintain it for people with outdated WordPress sites. And the plugin is still usefull for sites with outdated plugins that not obey get_user_locale(). 
<a href="https://make.wordpress.org/core/2016/11/07/user-admin-languages-and-locale-switching-in-4-7/" rel="nofollow ugc">More info</a>

Admin Language Per User

a must have for multilingual sites

Switch your backend administration panel in any installed language per user basis.

Simple Translation Remover vs Admin Language Per User