How do I have my control panel in English but my site locale to Dutch? I prefer my cp in English but I've noticed that it also sets the locale to "en_us" for the entire site. I need that locale to be "nl" since the site is in Dutch. Any idea how to achieve this?
This solutions works for any locale, even if you don't have it installed as a front-end locale.
It also works for Personal or Client Craft installs.

Add a translations file into craft/translations/xx.php named after the currently selected user locale or system locale for
Craft Personal installs and use this code to include any locale's translations you want. You can also customize it
further by overwriting select translations:

&lt;?php
namespace Craft;

if (craft()-&gt;request-&gt;isCpRequest())
{
    $en = (include '../craft/app/translations/en.php');
    $custom = array(
        'Globals' =&gt; 'I freak out!',
    );

    return array_merge($en, $custom);
}

return [];