SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    26625, 26815, 26814, 26813, 26812, 26811, 
    26810, 26809, 26808, 26807, 26806, 
    26805, 26804, 26803, 26802, 26801, 
    26800, 26799
  ) 
  AND feature_id IN (1071) 
  AND lang_code = 'en'

Query time 0.00126

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "2.00"
    },
    "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": 1,
      "rows_produced_per_join": 1,
      "filtered": "100.00",
      "using_index_for_skip_scan": true,
      "cost_info": {
        "read_cost": "1.90",
        "eval_cost": "0.10",
        "prefix_cost": "2.00",
        "data_read_per_join": "792"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`cscartdb`.`cscart_product_features_values`.`feature_id` = 1071) and (`cscartdb`.`cscart_product_features_values`.`product_id` in (26625,26815,26814,26813,26812,26811,26810,26809,26808,26807,26806,26805,26804,26803,26802,26801,26800,26799)) and (`cscartdb`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}