SELECT 
  f.*, 
  d.description 
FROM 
  cscart_form_options as f 
  LEFT JOIN cscart_form_descriptions as d ON d.object_id = f.element_id 
  AND d.lang_code = 'ja' 
WHERE 
  f.page_id = 30 
  AND f.status = 'A' 
ORDER BY 
  f.position

Query time 0.00005

JSON explain

{
  "query_block": {
    "select_id": 1,
    "read_sorted_file": {
      "filesort": {
        "sort_key": "f.position",
        "table": {
          "table_name": "f",
          "access_type": "ref",
          "possible_keys": ["page_id"],
          "key": "page_id",
          "key_length": "6",
          "used_key_parts": ["page_id", "status"],
          "ref": ["const", "const"],
          "rows": 9,
          "filtered": 100,
          "index_condition": "f.`status` = 'A'",
          "attached_condition": "f.page_id <=> 30 and f.`status` <=> 'A'"
        }
      }
    },
    "table": {
      "table_name": "d",
      "access_type": "eq_ref",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["object_id", "lang_code"],
      "ref": ["markins_test.f.element_id", "const"],
      "rows": 1,
      "filtered": 100,
      "attached_condition": "trigcond(d.lang_code = 'ja')"
    }
  }
}