The (new) determine_locale() may throw a notice

[azaozz]

Happens then there is a plugin in /mu-plugins that loads a textdomain and $_GET['wp_lang'] is not empty, like when trying to log in.

Caused by the global $pagenow. It is set after mu-plugins are loaded (in vars.php) but determine_locale() expects is to always be set.

[azaozz]

Introduced in [43776]. An ! empty( $GLOBALS['pagenow'] ) check would probably fix it.

Setting to 5.0.2 as a notice would break any JS output.

[pento]

In 44284:

i18n: Prevent a PHP warning when a mu-plugin loads a textdomain.

determine_locale() accesses the $pagenow global, but this is set after mu-plugins are loaded, so we need to check that it's been set.

Props swissspidy, azaozz.
See #45668.

[SergeyBiryukov]

In 44317:

i18n: Prevent a PHP warning when a mu-plugin loads a textdomain.

determine_locale() accesses the $pagenow global, but this is set after mu-plugins are loaded, so we need to check that it's been set.

Props swissspidy, azaozz.
Merges [44284] to trunk.
Fixes #45668.

[pento]

#45696 was marked as a duplicate.