Define string_lower() as a function that will use mb_strlower() if av…

…ailable, and fall back to strtolower() if not.

Update install_category_migrate() to use the new function; affects #9161, 9298.

admin/install_functions.php

@@ -58,7 +58,7 @@ function install_category_migrate() {
 	foreach( $t_data as $t_project_id => $t_categories ) {
 		$t_inserted = array();
 		foreach( $t_categories as $t_name => $t_true ) {
-			$t_lower_name = strtolower( $t_name );
+			$t_lower_name = string_lower( $t_name );
 			if ( !isset( $t_inserted[$t_lower_name] ) ) {
 				$query = "INSERT INTO $t_category_table ( name, project_id ) VALUES ( " . db_param() . ', ' . db_param() . ' )';
 				db_query_bound( $query, array( $t_name, $t_project_id ) );

core/string_api.php

@@ -37,6 +37,22 @@
 $g_cache_html_valid_tags = '';
 $g_cache_html_valid_tags_single_line = '';
 
+/**
+ * Return a string with all alphabetical characters converted to lowercase,
+ * using an appropriate multibyte implementation as available to system.
+ * @param string Input string
+ * @return string Lower cased string
+ */
+if ( function_exists( 'mb_strtolower' ) ) {
+	function string_lower( $p_string ) {
+			return mb_strtolower( $p_string );
+	}
+} else {
+	function string_lower( $p_string ) {
+			return strtolower( $p_string );
+	}
+}
+
 # ## --------------------
 # Preserve spaces at beginning of lines.
 # Lines must be separated by \n rather than <br />