SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    19933, 19934, 19935, 19936, 19937, 19938, 
    19939, 19940, 19941, 19942, 19943, 
    19944, 19945, 19946, 19947, 19948
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00047

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 (19933,19934,19935,19936,19937,19938,19939,19940,19941,19942,19943,19944,19945,19946,19947,19948) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}