SELECT 
  variant_id, 
  yml2_unit 
FROM 
  cscart_product_feature_variant_descriptions 
WHERE 
  variant_id IN (
    '1', '1313', '1298', '289', '1299', 
    '125', '126', '281', '504', '508', 
    '258', '1329', '453', '494', '236', 
    '462', '424', '239', '1297', '290', 
    '250', '251', '302', '383', '122', 
    '240', '121', '127', '149', '120', 
    '123', '152', '270', '234', '146', 
    '50', '57', '58', '147', '9', '15', 
    '18', '11', '6', '8', '30', '25', '26', 
    '1453', '426', '267', '507', '287', 
    '1303', '294', '262', '162', '263', 
    '421', '110', '264', '265', '422', 
    '1305', '282', '111', '260', '1300', 
    '54', '304', '303', '237'
  ) 
  AND lang_code = 'ru'

Query time 0.00105

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "50.41"
    },
    "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": 72,
      "rows_produced_per_join": 72,
      "filtered": "100.00",
      "index_condition": "((`test_uchur_k`.`cscart_product_feature_variant_descriptions`.`variant_id` in ('1','1313','1298','289','1299','125','126','281','504','508','258','1329','453','494','236','462','424','239','1297','290','250','251','302','383','122','240','121','127','149','120','123','152','270','234','146','50','57','58','147','9','15','18','11','6','8','30','25','26','1453','426','267','507','287','1303','294','262','162','263','421','110','264','265','422','1305','282','111','260','1300','54','304','303','237')) and (`test_uchur_k`.`cscart_product_feature_variant_descriptions`.`lang_code` = 'ru'))",
      "cost_info": {
        "read_cost": "43.21",
        "eval_cost": "7.20",
        "prefix_cost": "50.41",
        "data_read_per_join": "224K"
      },
      "used_columns": [
        "variant_id",
        "lang_code",
        "yml2_unit"
      ]
    }
  }
}