SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    13281, 13282, 13283, 13284, 13285, 13280
  ) 
  AND feature_id IN (
    595, 628, 627, 624, 625, 553, 626, 622, 
    623, 636, 637
  ) 
  AND lang_code = 'en'

Query time 0.00341

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "5.66"
    },
    "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": "PRIMARY",
      "used_key_parts": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "key_length": "15",
      "rows_examined_per_scan": 12,
      "rows_produced_per_join": 12,
      "filtered": "100.00",
      "using_index_for_skip_scan": true,
      "cost_info": {
        "read_cost": "4.47",
        "eval_cost": "1.20",
        "prefix_cost": "5.67",
        "data_read_per_join": "9K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`test2_gaseus`.`cscart_product_features_values`.`product_id` in (13281,13282,13283,13284,13285,13280)) and (`test2_gaseus`.`cscart_product_features_values`.`feature_id` in (595,628,627,624,625,553,626,622,623,636,637)) and (`test2_gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id feature_id variant_id
13280 553 1912
13281 553 1912
13282 553 1912
13283 553 1912
13284 553 1912
13285 553 1912
13280 595 1904
13281 595 2451
13282 595 1787
13283 595 1905
13284 595 1900
13285 595 1462
13280 622 2559
13281 622 2559
13282 622 2559
13283 622 2559
13284 622 2559
13285 622 2559
13280 623 2524
13281 623 2524
13282 623 2524
13283 623 2524
13284 623 2524
13285 623 2524
13280 624 1694
13281 624 1694
13282 624 1694
13283 624 1694
13284 624 1694
13285 624 1694
13280 625 2413
13281 625 2413
13282 625 2413
13283 625 2413
13284 625 2413
13285 625 2413
13280 626 1926
13281 626 1926
13282 626 1926
13283 626 1926
13284 626 1926
13285 626 1926
13280 627 2290
13281 627 2290
13282 627 2290
13283 627 2290
13284 627 2290
13285 627 2290
13280 628 1660
13281 628 1660
13282 628 1660
13283 628 1660
13284 628 1660
13285 628 1660
13280 636 2344
13281 636 2344
13282 636 2344
13283 636 2344
13284 636 2344
13285 636 2344
13280 637 2345
13281 637 2345
13282 637 2345
13283 637 2345
13284 637 2345
13285 637 2345