SELECT 
  product_id, 
  feature_id, 
  variant_id 
FROM 
  cscart_product_features_values 
WHERE 
  product_id IN (
    63431, 63432, 63433, 63434, 63435, 63436, 
    63437, 63438, 63439, 63440, 63441, 
    63442
  ) 
  AND feature_id IN (1480, 1461) 
  AND lang_code = 'en'

Query time 0.00148

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "2.26"
    },
    "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": 2,
      "rows_produced_per_join": 2,
      "filtered": "100.00",
      "using_index_for_skip_scan": true,
      "cost_info": {
        "read_cost": "2.06",
        "eval_cost": "0.20",
        "prefix_cost": "2.26",
        "data_read_per_join": "1K"
      },
      "used_columns": [
        "feature_id",
        "product_id",
        "variant_id",
        "lang_code"
      ],
      "attached_condition": "((`cscartdb`.`cscart_product_features_values`.`product_id` in (63431,63432,63433,63434,63435,63436,63437,63438,63439,63440,63441,63442)) and (`cscartdb`.`cscart_product_features_values`.`feature_id` in (1480,1461)) and (`cscartdb`.`cscart_product_features_values`.`lang_code` = 'en'))"
    }
  }
}