SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    20093, 20094, 20095, 20096, 20097, 20098, 
    20099, 20100, 20101, 20102, 20103, 
    20104, 20105, 20106, 20107, 20108
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00090

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 (20093,20094,20095,20096,20097,20098,20099,20100,20101,20102,20103,20104,20105,20106,20107,20108) and cscart_product_descriptions.lang_code = 'en'"
    }
  }
}