SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    431514, 431515, 431516, 431517, 431518, 
    431519, 431520, 431521, 431522, 431523, 
    431524, 431525, 431526, 431527, 431528, 
    431529, 431530, 431531, 431532, 431533, 
    431534, 431535, 431536, 431537
  ) 
  AND feature_id IN (626, 860) 
  AND lang_code = 'en'

Query time 0.00289

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "20.33"
    },
    "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": "lang_code",
      "used_key_parts": [
        "lang_code",
        "feature_id",
        "product_id"
      ],
      "key_length": "12",
      "rows_examined_per_scan": 48,
      "rows_produced_per_join": 48,
      "filtered": "100.00",
      "using_index": true,
      "cost_info": {
        "read_cost": "10.73",
        "eval_cost": "9.60",
        "prefix_cost": "20.33",
        "data_read_per_join": "37K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`webmarco`.`cscart_product_features_values`.`product_id` in (431514,431515,431516,431517,431518,431519,431520,431521,431522,431523,431524,431525,431526,431527,431528,431529,431530,431531,431532,431533,431534,431535,431536,431537)) and (`webmarco`.`cscart_product_features_values`.`feature_id` in (626,860)) and (`webmarco`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}