SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    7059, 7058, 7057, 6862, 3304, 6852, 3309, 
    6865, 6856, 6849, 3298, 3297, 6845, 
    3299, 6863, 6853, 3308, 3314, 6857, 
    3310, 6858, 3318
  ) 
  AND feature_id IN (
    595, 628, 624, 625, 553, 626, 622, 623, 
    627, 636, 637, 641
  ) 
  AND lang_code = 'en'

Query time 0.00439

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "59.70"
    },
    "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": 264,
      "rows_produced_per_join": 264,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "33.30",
        "eval_cost": "26.40",
        "prefix_cost": "59.70",
        "data_read_per_join": "204K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`gaseus`.`cscart_product_features_values`.`product_id` in (7059,7058,7057,6862,3304,6852,3309,6865,6856,6849,3298,3297,6845,3299,6863,6853,3308,3314,6857,3310,6858,3318)) and (`gaseus`.`cscart_product_features_values`.`feature_id` in (595,628,624,625,553,626,622,623,627,636,637,641)) and (`gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}