SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    10972, 10973, 10974, 10975, 10976, 10977, 
    10978, 10979, 10980, 10981, 10982, 
    10983, 10984, 10965, 10966, 10967, 
    10968, 10969, 10970, 10971
  ) 
  AND feature_id IN (553, 624, 623) 
  AND lang_code = 'en'

Query time 0.00302

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 (10972,10973,10974,10975,10976,10977,10978,10979,10980,10981,10982,10983,10984,10965,10966,10967,10968,10969,10970,10971)) and (`gaseus`.`cscart_product_features_values`.`feature_id` in (553,624,623)) and (`gaseus`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}