SELECT 
  p.*, 
  d.*, 
  images.promotion_image_id 
FROM 
  cscart_promotions as p 
  LEFT JOIN cscart_promotion_descriptions as d ON p.promotion_id = d.promotion_id 
  AND d.lang_code = 'ru' 
  LEFT JOIN cscart_promotion_images AS images ON images.promotion_id = p.promotion_id 
  AND images.lang_code = 'ru' 
WHERE 
  p.promotion_id = 199

Query time 0.00050

JSON explain

{
  "query_block": {
    "select_id": 1,
    "const_condition": "1",
    "nested_loop": [
      {
        "table": {
          "table_name": "p",
          "access_type": "const",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["promotion_id"],
          "ref": ["const"],
          "rows": 1,
          "filtered": 100
        }
      },
      {
        "table": {
          "table_name": "d",
          "access_type": "const",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["promotion_id", "lang_code"],
          "ref": ["const", "const"],
          "rows": 1,
          "filtered": 100
        }
      },
      {
        "table": {
          "table_name": "images",
          "access_type": "const",
          "possible_keys": ["promo"],
          "key": "promo",
          "key_length": "10",
          "used_key_parts": ["promotion_id", "lang_code"],
          "ref": ["const", "const"],
          "rows": 1,
          "filtered": 100
        }
      }
    ]
  }
}