SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    12869, 12870, 12871, 12872, 12873, 12874, 
    12875
  ) 
  AND feature_id IN (
    622, 626, 595, 628, 627, 624, 625, 553, 
    637, 623, 636
  ) 
  AND lang_code = 'en'

Query time 0.00482

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 (12869,12870,12871,12872,12873,12874,12875)) and (`test2_gaseus`.`cscart_product_features_values`.`feature_id` in (622,626,595,628,627,624,625,553,637,623,636)) and (`test2_gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}

Result

product_id feature_id variant_id
12869 553 1912
12870 553 1912
12871 553 1912
12872 553 1912
12873 553 1912
12874 553 1912
12875 553 1912
12869 595 1904
12870 595 2451
12871 595 2451
12872 595 2451
12873 595 1905
12874 595 1900
12875 595 2455
12869 622 2443
12870 622 2443
12871 622 2443
12872 622 2443
12873 622 2443
12874 622 2448
12875 622 2448
12869 623 2444
12870 623 2444
12871 623 2444
12872 623 2444
12873 623 2444
12874 623 2444
12875 623 2444
12869 624 1705
12870 624 1705
12871 624 1705
12872 624 1705
12873 624 1705
12874 624 1705
12875 624 1705
12869 625 2462
12870 625 2464
12871 625 2467
12872 625 2467
12873 625 2464
12874 625 2464
12875 625 2467
12869 626 2463
12870 626 2466
12871 626 2463
12872 626 2468
12873 626 2465
12874 626 2469
12875 626 2469
12869 627 2290
12870 627 2290
12871 627 2290
12872 627 2290
12873 627 2290
12874 627 2290
12875 627 2290
12869 628 1660
12870 628 1660
12871 628 1660
12872 628 1660
12873 628 1660
12874 628 1660
12875 628 1660
12869 636 2344
12870 636 2344
12871 636 2344
12872 636 2344
12873 636 2344
12874 636 2344
12875 636 2344
12869 637 2350
12870 637 2350
12871 637 2350
12872 637 2350
12873 637 2350
12874 637 2350
12875 637 2350