SELECT 
  a.code, 
  b.state 
FROM 
  cscart_states as a 
  LEFT JOIN cscart_state_descriptions as b ON b.state_id = a.state_id 
  AND b.lang_code = 'de' 
WHERE 
  a.country_code = 'AT' 
ORDER BY 
  b.state

Query time 0.00024

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.027413578,
    "filesort": {
      "sort_key": "b.state",
      "temporary_table": {
        "nested_loop": [
          {
            "table": {
              "table_name": "a",
              "access_type": "ref",
              "possible_keys": ["cs", "country_code"],
              "key": "cs",
              "key_length": "8",
              "used_key_parts": ["country_code"],
              "ref": ["const"],
              "loops": 1,
              "rows": 7,
              "cost": 0.009427625,
              "filtered": 100,
              "index_condition": "a.country_code = 'AT'"
            }
          },
          {
            "table": {
              "table_name": "b",
              "access_type": "eq_ref",
              "possible_keys": ["PRIMARY"],
              "key": "PRIMARY",
              "key_length": "9",
              "used_key_parts": ["state_id", "lang_code"],
              "ref": ["cscart.a.state_id", "const"],
              "loops": 7,
              "rows": 1,
              "cost": 0.013536782,
              "filtered": 100,
              "attached_condition": "trigcond(b.lang_code = 'de')"
            }
          }
        ]
      }
    }
  }
}