Soft-deprecate load_*_textdomain() functions

[swissspidy]

(Soft) deprecate load_plugin_textdomain() and load_theme_textdomain() and rely solely on the just-in-time loading and WP_Textdomain_Registry.

This would avoid any _doing_it_wrong messages for plugins still using load_plugin_textdomain(), which seems to be the most common case and affects even very big plugins. So it would drastically reduce the noise.

It would still trigger a _doing_it_wrong message if accidentally causing the just-in-time loading too early.

Trac ticket: https://core.trac.wordpress.org/ticket/44937

---

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[github-actions]

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[swissspidy]

Only 1 failing test, that sounds doable :-)

1) WP_Test_REST_Themes_Controller::test_theme_tags
Failed asserting that two arrays are identical.
--- Expected
+++ Actual
@@ @@
 Array &0 (
-    0 => 'holiday'
+    0 => 'Holiday'
     1 => 'custom-menu'
 )

/var/www/tests/phpunit/tests/rest-api/rest-themes-controller.php:585

[swissspidy]

OK when I remove the now unused plugin_locale and theme_locale filters a couple of more tests are failing, because they hook into those filters. But nothing is actually broken.

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Props swissspidy, sergeybiryukov, mukesh27.

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[mukeshpanchal27]

Q: Many plugins uses the filter https://wpdirectory.net/search/01J96KCH95TBF66SB7N0PKAFM2. We are going to remove these?

[swissspidy]

With the removal of this code there is nothing this filter could be used for anymore. If a plugin is hooking into that filter it simply won't do anything.

We could consider using apply_filters_deprecated without actually using the filter. There's prior art here:

wordpress-develop/src/wp-includes/rest-api/class-wp-rest-server.php

Lines 333 to 352 in 1ec0abb

	/**
	* Filters whether the REST API is enabled.
	*
	* @since 4.4.0
	* @deprecated 4.7.0 Use the {@see 'rest_authentication_errors'} filter to
	* restrict access to the REST API.
	*
	* @param bool $rest_enabled Whether the REST API is enabled. Default true.
	*/
	apply_filters_deprecated(
	'rest_enabled',
	array( true ),
	'4.7.0',
	'rest_authentication_errors',
	sprintf(
	/* translators: %s: rest_authentication_errors */
	__( 'The REST API can no longer be completely disabled, the %s filter can be used to restrict access to the API, instead.' ),
	'rest_authentication_errors'
	)
	);

[swissspidy]

On second thought, I don't think apply_filters_deprecated makes sense though. If you're developing a custom plugin there's a legitimate use for using load_plugin_textdomain(). You shouldn't be faced with a deprecation warning even if you use it properly.

[swissspidy]

Committed in https://core.trac.wordpress.org/changeset/59157