add en_US to the list of languages
make it possible to activate en_US language
Add functionality to filter list of languages
remove empty line added by mistake
improve test for `wp core language --<field>=<value>`
remove underscores from methods names
Revert "improve test for `wp core language --<field>=<value>`"

This reverts commit 6952bc4b859655afb46cd679ab60998180224aed.
Revert "remove empty line added by mistake"

This reverts commit 1a571218f1a2a195b2311f5ff46d59176f9f74d7.
Revert "Add functionality to filter list of languages"

This reverts commit 489458a0f00a9ed2b5e53e92cf9c4558c7614b8f.
Merge pull request #1413 from rodrigoprimo/language-en-us

Add en_US language to `wp core language`