English (US), or “en_US” for short, is the default localeLocale Locale = language version, often a combination of a language code and a region code, for instance es_MX denotes Spanish as it’s used in Mexico. A list of all locales supported by WordPress in https://make.wordpress.org/polyglots/teams/ in WordPress.

There is no locale team for en_US in WordPress Polyglots’ team, since we don’t translate to and not from en_US.

List of translation teams.