By default "en" language item is protected and it is used/configured in all the Sitecore default sites like shell, login, modules-shell and modules-website.
<site name="shell" language="en" contentLanguage="en" .../>
<site name="login" language="en" .../>
<site name="modules_shell" language="en" .../>
<site name="modules_website" language="en" .../>
So when you unprotect and set Language write rights to a specific role then you are actually overwriting the Sitecore's inbuilt security.
For ex. If you create a Sitecore user with "Sitecore Developer" role then the default behavior is the user could able to edit the templates and items under system etc. But when you overwrite the security at "en" language item by enabling the language write only to a specific new role and restrict for "sitecore\Everyone" then all the Sitecore inbuilt security will be messed up. The Sitecore Developer user could not able to edit the templates. This is just a sample and there may be many scenarios where you will be overwriting the Sitecore inbuilt security/setup.
So if you are having any custom changes on top of "en" language item then I would suggest creating a new language like en-GB or en-US or anything relevant to your requirement and leave the default "en" item without any change.