SELECT 
  variant_id, 
  yml2_unit 
FROM 
  cscart_product_feature_variant_descriptions 
WHERE 
  variant_id IN (
    '1', '125', '211', '220', '223', '226', 
    '227', '233', '230', '231', '236', 
    '239', '241', '242', '244', '243', 
    '245', '247', '248', '250', '251', 
    '122', '121', '127', '149', '246', 
    '120', '123', '152', '234', '146', 
    '228', '50', '58', '147', '41', '40', 
    '6', '249', '237', '238', '98', '217', 
    '232', '170', '165'
  ) 
  AND lang_code = 'ru'

Query time 0.00056

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "32.21"
    },
    "table": {
      "table_name": "cscart_product_feature_variant_descriptions",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "variant_id",
        "lang_code"
      ],
      "key_length": "9",
      "rows_examined_per_scan": 46,
      "rows_produced_per_join": 46,
      "filtered": "100.00",
      "index_condition": "((`test_uchur_k`.`cscart_product_feature_variant_descriptions`.`variant_id` in ('1','125','211','220','223','226','227','233','230','231','236','239','241','242','244','243','245','247','248','250','251','122','121','127','149','246','120','123','152','234','146','228','50','58','147','41','40','6','249','237','238','98','217','232','170','165')) and (`test_uchur_k`.`cscart_product_feature_variant_descriptions`.`lang_code` = 'ru'))",
      "cost_info": {
        "read_cost": "27.61",
        "eval_cost": "4.60",
        "prefix_cost": "32.21",
        "data_read_per_join": "143K"
      },
      "used_columns": [
        "variant_id",
        "lang_code",
        "yml2_unit"
      ]
    }
  }
}