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wp-content/plugins/jetpack/extensions/shared/cdn-locale.php

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+<?php
+/**
+ * Shared locale helper for extensions that load assets from widgets.wp.com.
+ *
+ * Used by CDN-based loaders (Image Studio, AI Sidebar) that need to map the
+ * current user's WordPress locale to the ISO 639 language code used by the
+ * widgets.wp.com translation files at languages/{code}-v1.js.
+ *
+ * @package automattic/jetpack
+ */
+
+namespace Automattic\Jetpack\Extensions\Shared;
+
+if ( ! defined( 'ABSPATH' ) ) {
+	exit( 0 );
+}
+
+/**
+ * Determine the ISO 639 locale code for the current user.
+ *
+ * Normalizes the WordPress user locale to match widgets.wp.com translation
+ * file naming. Preserves region for a small set of locales where the region
+ * is meaningful (pt_br, zh_tw, zh_cn); strips the region for all others;
+ * falls back to 'en' when the locale is empty.
+ *
+ * @return string The ISO 639 language code, defaulting to 'en'.
+ */
+function determine_iso_639_locale(): string {
+	$language = get_user_locale();
+	$language = strtolower( $language );
+
+	if ( in_array( $language, array( 'pt_br', 'pt-br', 'zh_tw', 'zh-tw', 'zh_cn', 'zh-cn' ), true ) ) {
+		$language = str_replace( '_', '-', $language );
+	} else {
+		$language = preg_replace( '/([-_].*)$/i', '', $language );
+	}
+
+	if ( empty( $language ) ) {
+		return 'en';
+	}
+
+	return $language;
+}