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'))"
    }
  }
}