SELECT 
  variant_id, 
  yml2_unit 
FROM 
  cscart_product_feature_variant_descriptions 
WHERE 
  variant_id IN (
    '1263', '1301', '1304', '1533', '1441', 
    '1468', '1470', '1443', '1469', '1474', 
    '1465', '1535', '1537', '1440', '1471', 
    '1453', '1452', '1467', '1472', '1425', 
    '1424', '1428', '1429', '1433'
  ) 
  AND lang_code = 'ru'

Query time 0.00045

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "table_name": "cscart_product_feature_variant_descriptions",
      "access_type": "range",
      "possible_keys": ["PRIMARY"],
      "key": "PRIMARY",
      "key_length": "9",
      "used_key_parts": ["variant_id", "lang_code"],
      "rows": 24,
      "filtered": 100,
      "index_condition": "cscart_product_feature_variant_descriptions.variant_id in ('1263','1301','1304','1533','1441','1468','1470','1443','1469','1474','1465','1535','1537','1440','1471','1453','1452','1467','1472','1425','1424','1428','1429','1433') and cscart_product_feature_variant_descriptions.lang_code = 'ru'"
    }
  }
}