Moment localized date formats broken

[mattheu]

Describe the bug

If you use moment to display a date, you can pass a localised date format. e.g. LLL moment will format a date like September 4, 1986 8:30 PM. See moment docs: https://momentjs.com/docs/#/displaying/

However in the WP admin this does not work. You get the following result: F j, 2018 g:i pm

This is a regression and worked as expected before Gutenberg version 4.5 - I believe it was broken in this commit: #11938.

Whilst investigating this issue - I see there is some handling of these localised date formats in wp.date package. If the expectation is that I should only use wp.date and never use the globally available copy of moment, then perhaps it should not be available to use? Otherwise I would expect this to work.

To Reproduce

1. From a post edit screen, open the browser console.
2. Type moment().format('LLL');
3. See incorrect result.
4. If you do the same on momentjs.com you see the expected behaviour.

Expected behavior
The code moment().format('LLL') should work as expected displaying "Month name, day of month, year, time" and also allow this to be localised.

[waviaei]

I followed the same step, and reproduced the issue.

Tested under:

• Mac OS Mojave 10.14.2
• Chrome 70.0.3538.110
• WordPress 5.0 (en_US)
• Theme: Twentynineteen

On moment.js, expected behaviour

[noisysocks]

Am able to confirm this still happens on current Gutenberg master. It might be that we're not properly localising this moment string, see https://core.trac.wordpress.org/ticket/47373.