Use translated variable for test string

Test should be educative, added english translation and pronounciation.

library/alloc/tests/string.rs

@@ -271,8 +271,8 @@ fn test_split_off_past_end() {
 #[test]
 #[should_panic]
 fn test_split_off_mid_char() {
-    let mut orig = String::from("山");
-    let _ = orig.split_off(1);
+    let mut shan = String::from("山");
+    let _broken_mountain = shan.split_off(1);
 }
 
 #[test]