Source

File: wp-includes/class.wp-scripts.php

public function localize( $handle, $object_name, $l10n ) {
		if ( 'jquery' === $handle ) {
			$handle = 'jquery-core';
		}

		if ( is_array( $l10n ) && isset( $l10n['l10n_print_after'] ) ) { // back compat, preserve the code in 'l10n_print_after' if present.
			$after = $l10n['l10n_print_after'];
			unset( $l10n['l10n_print_after'] );
		}

		foreach ( (array) $l10n as $key => $value ) {
			if ( ! is_scalar( $value ) ) {
				continue;
			}

			$l10n[ $key ] = html_entity_decode( (string) $value, ENT_QUOTES, 'UTF-8' );
		}

		$script = "var $object_name = " . wp_json_encode( $l10n ) . ';';

		if ( ! empty( $after ) ) {
			$script .= "\n$after;";
		}

		$data = $this->get_data( $handle, 'data' );

		if ( ! empty( $data ) ) {
			$script = "$data\n$script";
		}

		return $this->add_data( $handle, 'data', $script );
	}