Media grid details: Load large images instead of originals, if available.

fixes #29498.

Built from https://develop.svn.wordpress.org/trunk@29704


git-svn-id: http://core.svn.wordpress.org/trunk@29478 1a063a9b-81f0-0310-95a4-ce76da25c4cd
i18n: Skip language chooser for localized packages.

Also fixes the install.php welcome string, which was not bring printed.

fixes #29487.

Built from https://develop.svn.wordpress.org/trunk@29705


git-svn-id: http://core.svn.wordpress.org/trunk@29479 1a063a9b-81f0-0310-95a4-ce76da25c4cd