Multisite: Can't set en_US for language, when creating a new site

[arkimedia]

Problem description:

1. I have a multisite where default language is set to Finnish (fi) from the network settings, so that get_site_option('WPLANG') returns 'fi'.

2. I want to create a new site and use en_US as a language.

3. If I choose "en_US" from the language chooser in site-new.php, $_POST['WPLANG'] doesn't contain any language.

4. Because $_POST['WPLANG'] is empty, no language is passed to the wpmu_create_blog function.

5. If no language is passed wpmu_create_blog function, it uses network default, which in this case is 'fi'.add_option( 'WPLANG', get_site_option( 'WPLANG' ) );

This isn't a problem if the network default language is en_US, but causes problems in localized multisites.

[ocean90]

Hello @arkimedia, thanks for the report. Looks like we need to replace an empty() check with isset().

The language chooser was introduced in [33920].

[ocean90]

#36360 was marked as a duplicate.

[ocean90]

In 38655:

Multisite: Allow to set the site language of a new site to English.

An empty string in WPLANG is used to define the site language as en_US. The ! empty() check didn't catch this case so that wpmu_create_blog() fell back to the network setting.

Fixes #36918.

[arkimedia]

Tested this with 4.7 beta 1 and issue seems to be fixed. Thank you for the patch @ocean90.