SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    19565, 19566, 19567, 19568, 19569, 19570, 
    19571, 19572, 19573, 19574, 19575, 
    19576, 19577, 19578, 19579, 19580
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00340

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 (19565,19566,19567,19568,19569,19570,19571,19572,19573,19574,19575,19576,19577,19578,19579,19580) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}