SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    13951, 13952, 13953, 13954, 13955, 13956, 
    13957, 13958, 13959, 13960, 13961, 
    13962
  ) 
  AND cscart_product_descriptions.lang_code = 'en'

Query time 0.00016

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost": 0.0216566,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_product_descriptions",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "product_id"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["product_id", "lang_code"],
          "loops": 1,
          "rows": 12,
          "cost": 0.0216566,
          "filtered": 100,
          "attached_condition": "cscart_product_descriptions.product_id in (13951,13952,13953,13954,13955,13956,13957,13958,13959,13960,13961,13962) and cscart_product_descriptions.lang_code = 'en'"
        }
      }
    ]
  }
}