SELECT 
  cscart_product_descriptions.product_id, 
  cscart_product_descriptions.unit_name 
FROM 
  cscart_product_descriptions 
WHERE 
  cscart_product_descriptions.product_id IN (
    8760, 8764, 8766, 8767, 8771, 8773, 8774, 
    8775, 8776, 8782, 8783, 8784, 8786, 
    8787, 8788, 8789
  ) 
  AND cscart_product_descriptions.lang_code = 'ru'

Query time 0.00041

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 (8760,8764,8766,8767,8771,8773,8774,8775,8776,8782,8783,8784,8786,8787,8788,8789) and cscart_product_descriptions.lang_code = 'ru'"
    }
  }
}