SELECT 
  variant_id, 
  yml2_unit 
FROM 
  cscart_product_feature_variant_descriptions 
WHERE 
  variant_id IN (
    '1661', '597', '1', '441', '1634', '429', 
    '433', '513', '1805', '1667', '1662', 
    '1633', '1619', '460', '447', '122', 
    '121', '440', '127', '439', '1349', 
    '362', '438', '149', '246', '120', 
    '1668', '1804', '430', '448', '1620', 
    '442', '1663', '1623', '1635', '1630', 
    '1664', '146', '431', '446', '59', 
    '147', '98', '280', '1637', '1627', 
    '1629', '170', '1628', '165'
  ) 
  AND lang_code = 'ru'

Query time 0.00061

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "35.01"
    },
    "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": 50,
      "rows_produced_per_join": 50,
      "filtered": "100.00",
      "index_condition": "((`test_uchur_k`.`cscart_product_feature_variant_descriptions`.`variant_id` in ('1661','597','1','441','1634','429','433','513','1805','1667','1662','1633','1619','460','447','122','121','440','127','439','1349','362','438','149','246','120','1668','1804','430','448','1620','442','1663','1623','1635','1630','1664','146','431','446','59','147','98','280','1637','1627','1629','170','1628','165')) and (`test_uchur_k`.`cscart_product_feature_variant_descriptions`.`lang_code` = 'ru'))",
      "cost_info": {
        "read_cost": "30.01",
        "eval_cost": "5.00",
        "prefix_cost": "35.01",
        "data_read_per_join": "155K"
      },
      "used_columns": [
        "variant_id",
        "lang_code",
        "yml2_unit"
      ]
    }
  }
}