SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    22399, 22400, 22401, 22402, 22403, 22404, 
    22405, 22406, 22407, 22408, 22409, 
    22410, 22411, 22412, 22413, 22414
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00031

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_descriptions",
      "access_type": "range",
      "possible_keys": ["PRIMARY", "product_id", "idx_product_lang"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["product_id", "lang_code"],
      "rows": 16,
      "filtered": 100,
      "index_condition": "cscart_product_descriptions.product_id in (22399,22400,22401,22402,22403,22404,22405,22406,22407,22408,22409,22410,22411,22412,22413,22414) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}