From afd88c4ac75720caf685649d9a455e9998dcff8a Mon Sep 17 00:00:00 2001
From: Pascal Birchler <pascal.birchler@gmail.com>
Date: Fri, 26 May 2023 17:57:23 +0000
Subject: [PATCH] I18N: Refactor `determine_locale()` for performance and
 readability.

Refactors the function to avoid unnecessary `get_locale()` calls and slightly improve performance, while keeping it readable.

Adds tests.

Props Cybr, spacedmonkey, swissspidy.
Fixes #58317.
Built from https://develop.svn.wordpress.org/trunk@55862


git-svn-id: http://core.svn.wordpress.org/trunk@55374 1a063a9b-81f0-0310-95a4-ce76da25c4cd
---
 wp-includes/l10n.php    | 36 ++++++++++++++++--------------------
 wp-includes/version.php |  2 +-
 2 files changed, 17 insertions(+), 21 deletions(-)

diff --git a/wp-includes/l10n.php b/wp-includes/l10n.php
index 448a233fa8..080007b869 100644
--- a/wp-includes/l10n.php
+++ b/wp-includes/l10n.php
@@ -132,30 +132,26 @@ function determine_locale() {
 	 */
 	$determined_locale = apply_filters( 'pre_determine_locale', null );
 
-	if ( ! empty( $determined_locale ) && is_string( $determined_locale ) ) {
+	if ( $determined_locale && is_string( $determined_locale ) ) {
 		return $determined_locale;
 	}
 
-	$determined_locale = get_locale();
-
-	if ( is_admin() ) {
+	if (
+		isset( $GLOBALS['pagenow'] ) && 'wp-login.php' === $GLOBALS['pagenow'] &&
+		( ! empty( $_GET['wp_lang'] ) || ! empty( $_COOKIE['wp_lang'] ) )
+	) {
+		if ( ! empty( $_GET['wp_lang'] ) ) {
+			$determined_locale = sanitize_locale_name( $_GET['wp_lang'] );
+		} else {
+			$determined_locale = sanitize_locale_name( $_COOKIE['wp_lang'] );
+		}
+	} else if (
+		( isset( $_GET['_locale'] ) && 'user' === $_GET['_locale'] && wp_is_json_request() ) ||
+		is_admin()
+	) {
 		$determined_locale = get_user_locale();
-	}
-
-	if ( isset( $_GET['_locale'] ) && 'user' === $_GET['_locale'] && wp_is_json_request() ) {
-		$determined_locale = get_user_locale();
-	}
-
-	$wp_lang = '';
-
-	if ( ! empty( $_GET['wp_lang'] ) ) {
-		$wp_lang = sanitize_locale_name( wp_unslash( $_GET['wp_lang'] ) );
-	} elseif ( ! empty( $_COOKIE['wp_lang'] ) ) {
-		$wp_lang = sanitize_locale_name( wp_unslash( $_COOKIE['wp_lang'] ) );
-	}
-
-	if ( ! empty( $wp_lang ) && ! empty( $GLOBALS['pagenow'] ) && 'wp-login.php' === $GLOBALS['pagenow'] ) {
-		$determined_locale = $wp_lang;
+	} else {
+		$determined_locale = get_locale();
 	}
 
 	/**
diff --git a/wp-includes/version.php b/wp-includes/version.php
index ebbdb952e7..1bffcbb766 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.3-alpha-55861';
+$wp_version = '6.3-alpha-55862';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.