The server is returning data in a rather strange format which is encoded JSON data inside a JSON structure. But the character encoding is only done once.

decode_json includes a UTF-8 decoding step. Since your code is using it twice, it is trying to do the UTF-8 decode twice in addition to the JSON decoding.

If you replace the second decode_json call with a from_json call, it should avoid the additional broken character decoding. It may be preferable to change all of the JSON parsing calls with from_json for consistency, and do the UTF-8 decoding yourself before doing JSON parsing. This can be done with decode_utf8 from Encode.