SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    7496, 7497, 7500, 7501, 7506, 7507, 7528, 
    7529, 5219, 1516, 5217, 5216, 3728, 
    5215, 5218, 1513, 1512, 1514, 1511, 
    1515, 5231, 5229, 514, 3730, 5228, 5230, 
    1530, 1527, 3675, 1528, 1526, 1529, 
    5214, 5212, 5211, 3727, 5210, 5213, 
    1510, 1507, 1506, 1508, 1505, 1509, 
    5236, 5234, 5233, 3731, 5232, 5235, 
    1536, 1533, 1532, 1534, 1531, 1535
  ) 
  AND feature_id IN (
    627, 623, 622, 626, 553, 625, 624, 628, 
    595
  ) 
  AND lang_code = 'en'

Query time 0.00859

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "113.45"
    },
    "table": {
      "table_name": "cscart_product_features_values",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY",
        "fl",
        "lang_code",
        "product_id",
        "fpl",
        "idx_product_feature_variant_id"
      ],
      "key": "idx_product_feature_variant_id",
      "used_key_parts": [
        "product_id",
        "feature_id",
        "lang_code"
      ],
      "key_length": "12",
      "rows_examined_per_scan": 504,
      "rows_produced_per_join": 504,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "63.05",
        "eval_cost": "50.40",
        "prefix_cost": "113.45",
        "data_read_per_join": "389K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`gaseus`.`cscart_product_features_values`.`product_id` in (7496,7497,7500,7501,7506,7507,7528,7529,5219,1516,5217,5216,3728,5215,5218,1513,1512,1514,1511,1515,5231,5229,514,3730,5228,5230,1530,1527,3675,1528,1526,1529,5214,5212,5211,3727,5210,5213,1510,1507,1506,1508,1505,1509,5236,5234,5233,3731,5232,5235,1536,1533,1532,1534,1531,1535)) and (`gaseus`.`cscart_product_features_values`.`feature_id` in (627,623,622,626,553,625,624,628,595)) and (`gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}