Add user language preference to 'Add new user' form

[barryceelen]

Existing users can select an admin language. Perhaps allow preselecting a language on the user edit screen may be helpful.

[johnbillion]

Makes sense. We did the same thing for sites in #33528.

[barryceelen]

38665.diff adds the language dropdown to the 'Add User' form.

Setting $user->locale is moved outside of the $update conditional.
Also removes setting $user->locale = ''. Unsure why that was there in the first place?

The language select is only shown if !is_multisite(). Is that correct?

[johnbillion]

Need to consider that there's also the ability to add a user to a site from the Network Admin -> Sites -> Edit -> Users screen.

[desrosj]

The most recent patch needs to be refreshed.

[johnbillion]

Updated the patch with changes which means the UI and behaviour of the dropdown now matches that of the one used when editing a user.

[johnbillion]

Confirmed that the welcome email sent to the user is sent in their own language.

[johnbillion]

In 47516:

Users: Add a user language preference option to the "Add New User" form.

This uses the same language selection control as the user editing screen and allows new users to be invited to a site in their own language.

Props barryceelen, johnbillion

Fixes #38665

[SergeyBiryukov]

In 47519:

Coding Standards: Fix WPCS issues in [47516].

See #38665.

[SergeyBiryukov]

In 47520:

Coding Standards: Remove some extra tabs in wp-admin/user-new.php.

Follow-up to [47516], [47519].

See #38665.

[johnbillion]

This has broken the ability for the user to change their language from the user profile editing screen. $user->locale always gets set to an empty string.

[afercia]

Looking at 38665.3.diff​, I'd like to suggest to add an inline comment where $user->locale is set to empty string. That may help avoid the same mistake in the future, as it's not immediately clear why it's needed. See

Also removes setting $user->locale = . Unsure why that was there in the first place?

[johnbillion]

[47739] missed this ticket.