SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    10985, 10986, 10987, 10988, 10989, 10990, 
    10991, 10992, 10993, 10994, 10995, 
    10996, 10997, 10998, 10999, 11000, 
    11001, 11002, 11003, 11004
  ) 
  AND feature_id IN (553, 624, 623) 
  AND lang_code = 'en'

Query time 0.00275

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "14.02"
    },
    "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": 60,
      "rows_produced_per_join": 60,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "8.02",
        "eval_cost": "6.00",
        "prefix_cost": "14.02",
        "data_read_per_join": "46K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`gaseus`.`cscart_product_features_values`.`product_id` in (10985,10986,10987,10988,10989,10990,10991,10992,10993,10994,10995,10996,10997,10998,10999,11000,11001,11002,11003,11004)) and (`gaseus`.`cscart_product_features_values`.`feature_id` in (553,624,623)) and (`gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}