Default timezone for new sites in WP multisite

[moreauf]

In WordPress Multisite, the super admin may set a default language for all newly created sites but not a default timezone. As a matter of fact, the timezone for new sites is taken from translation string "0" (context string "default GMT offset or timezone string"). ​Relevant code

Unfortunately, language is not location. It's entirely possible for a community using WordPress multisite to use a language while not being physically based in the usual timezone for said language. Furthermore, many language are spread all over the world.

For that reason I think it would be more correct to decouple default timezone from translation files and add a "default timezone for new sites" setting for multisite installations.

[henry.wright]

I agree language isn't location.

The translated string may be a numeric offset or a database name such as "Africa/Addis_Ababa". I think the solution should continue to support translations like this if they exist but the primary way to set the default shouldn't be gettext.

[henry.wright]

@jeremyfelt @swissspidy and I discussed this at WordCamp Europe. We think introducing a popular_option_timezone_string filter would help separate language and location in this case. Please find a patch attached

[henry.wright]

43802.2.diff fixes the filter name