SELECT 
  c.category_id, 
  d.category 
FROM 
  cscart_categories as c 
  LEFT JOIN cscart_category_descriptions as d ON c.category_id = d.category_id 
WHERE 
  c.parent_id = 1780

Query time 0.00026

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "c",
      "access_type": "ref",
      "possible_keys": ["parent"],
      "key": "parent",
      "key_length": "3",
      "used_key_parts": ["parent_id"],
      "ref": ["const"],
      "rows": 10,
      "filtered": 100,
      "using_index": true
    },
    "table": {
      "table_name": "d",
      "access_type": "ref",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "3",
      "used_key_parts": ["category_id"],
      "ref": ["cscart_migrate.c.category_id"],
      "rows": 1,
      "filtered": 100
    }
  }
}

Result