SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    12863, 12865, 12867, 12861, 12864, 12868, 
    12860, 12859, 12858, 12857, 12856, 
    12855, 12854, 12853, 12852, 12851, 
    12850, 12866, 12862
  ) 
  AND feature_id IN (
    622, 623, 636, 637, 626, 553, 625, 624, 
    627, 628, 595
  ) 
  AND lang_code = 'en'

Query time 0.00428

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "7.83"
    },
    "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": 20,
      "rows_produced_per_join": 20,
      "filtered": "100.00",
      "using_index_for_skip_scan": true,
      "cost_info": {
        "read_cost": "5.84",
        "eval_cost": "2.00",
        "prefix_cost": "7.84",
        "data_read_per_join": "15K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`test2_gaseus`.`cscart_product_features_values`.`product_id` in (12863,12865,12867,12861,12864,12868,12860,12859,12858,12857,12856,12855,12854,12853,12852,12851,12850,12866,12862)) and (`test2_gaseus`.`cscart_product_features_values`.`feature_id` in (622,623,636,637,626,553,625,624,627,628,595)) and (`test2_gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id feature_id variant_id
12850 553 1912
12851 553 1912
12852 553 1912
12853 553 1912
12854 553 1912
12855 553 1912
12856 553 1912
12857 553 1912
12858 553 1912
12859 553 1912
12860 553 1912
12861 553 1912
12862 553 1912
12863 553 1912
12864 553 1912
12865 553 1912
12866 553 1912
12867 553 1912
12868 553 1912
12850 595 1904
12851 595 2000
12852 595 2451
12853 595 2451
12854 595 2451
12855 595 1787
12856 595 1905
12857 595 1900
12858 595 2455
12859 595 2455
12860 595 2455
12861 595 2455
12862 595 1462
12863 595 2457
12864 595 1972
12865 595 1902
12866 595 1902
12867 595 2075
12868 595 1995
12850 622 2443
12851 622 2448
12852 622 2443
12853 622 2443
12854 622 2443
12855 622 2443
12856 622 2443
12857 622 2448
12858 622 2448
12859 622 2448
12860 622 2448
12861 622 2448
12862 622 2443
12863 622 2448
12864 622 2443
12865 622 2448
12866 622 2448
12867 622 2448
12868 622 2448
12850 623 2444
12851 623 2444
12852 623 2444
12853 623 2444
12854 623 2444
12855 623 2444
12856 623 2444
12857 623 2444
12858 623 2444
12859 623 2444
12860 623 2444
12861 623 2444
12862 623 2444
12863 623 2444
12864 623 2444
12865 623 2444
12866 623 2444
12867 623 2444
12868 623 2444
12850 624 1694
12851 624 2447
12852 624 1694
12853 624 1694
12854 624 1694
12855 624 1694
12856 624 1694
12857 624 1694
12858 624 1694
12859 624 1694
12860 624 1694
12861 624 1694
12862 624 1694
12863 624 1694
12864 624 1694
12865 624 1992
12866 624 1992
12867 624 1992
12868 624 1992
12850 625 2122
12851 625 2413
12852 625 2122
12853 625 2452
12854 625 2452
12855 625 2122
12856 625 2122
12857 625 2122
12858 625 2122
12859 625 2452
12860 625 2452
12861 625 2452
12862 625 2122
12863 625 2122
12864 625 2122
12865 625 2139
12866 625 2452
12867 625 2413
12868 625 2413
12850 626 2445
12851 626 2449
12852 626 2445
12853 626 2453
12854 626 2454
12855 626 2445
12856 626 2445
12857 626 2445
12858 626 2445
12859 626 2453
12860 626 2454
12861 626 2456
12862 626 2445
12863 626 2445
12864 626 2445
12865 626 2458
12866 626 2460
12867 626 2449
12868 626 2449
12850 627 2290
12851 627 2290
12852 627 2290
12853 627 2290
12854 627 2290
12855 627 2290
12856 627 2290
12857 627 2290
12858 627 2290
12859 627 2290
12860 627 2290
12861 627 2290
12862 627 2290
12863 627 2290
12864 627 2290
12865 627 2290
12866 627 2290
12867 627 2290
12868 627 2290
12850 628 1660
12851 628 1660
12852 628 1660
12853 628 1660
12854 628 1660
12855 628 1660
12856 628 1660
12857 628 1660
12858 628 1660
12859 628 1660
12860 628 1660
12861 628 1660
12862 628 1660
12863 628 1660
12864 628 1660
12865 628 1660
12866 628 1660
12867 628 1660
12868 628 1660
12850 636 2344
12851 636 2344
12852 636 2344
12853 636 2344
12854 636 2344
12855 636 2344
12856 636 2344
12857 636 2344
12858 636 2344
12859 636 2344
12860 636 2344
12861 636 2344
12862 636 2344
12863 636 2344
12864 636 2344
12865 636 2344
12866 636 2344
12867 636 2344
12868 636 2344
12850 637 2345
12851 637 2345
12852 637 2345
12853 637 2350
12854 637 2350
12855 637 2345
12856 637 2345
12857 637 2345
12858 637 2345
12859 637 2350
12860 637 2350
12861 637 2350
12862 637 2345
12863 637 2345
12864 637 2345
12865 637 2345
12866 637 2345
12867 637 2345
12868 637 2345