src/Tools/Code/code_scala.ML

 val literals = let
   fun char_scala c = if c = "'" then "\\'"
     else if c = "\"" then "\\\""
     else if c = "\\" then "\\\\"
     else let val k = ord c
-    in if k < 32 orelse k > 126 then "\\" ^ radixstring (8, "0", k) else c end
+    in if k < 32 orelse k > 126
+    then "\\u" ^ align_right "0" 4 (radixstring (8, "0", k)) else c end
   fun numeral_scala k =
     if ~2147483647 < k andalso k <= 2147483647
     then signed_string_of_int k
     else quote (signed_string_of_int k)
 in Literals {