SELECT 
  pfv.feature_id, 
  pfv.product_id, 
  pfv.variant_id, 
  fv.position, 
  fvd.variant 
FROM 
  cscart_product_features_values AS pfv 
  INNER JOIN cscart_product_feature_variants AS fv ON pfv.feature_id = fv.feature_id 
  AND pfv.variant_id = fv.variant_id 
  INNER JOIN cscart_product_feature_variant_descriptions AS fvd ON pfv.variant_id = fvd.variant_id 
  AND fvd.lang_code = 'en' 
WHERE 
  pfv.feature_id IN (
    1482, 265, 259, 258, 289, 1207, 288, 287, 
    1466, 1461, 266, 271
  ) 
  AND pfv.product_id IN (
    20840, 20730, 20720, 20748, 20970, 20760, 
    14099, 20712, 20713, 15481, 16046, 
    16055, 17412, 20954, 20743, 20765, 
    16100, 16036, 16037, 62954, 20953, 
    16098, 16035, 57917, 57934, 14136, 
    14111, 16045, 57946, 57947, 14116, 
    57916, 21010
  ) 
  AND pfv.lang_code = 'en'

Query time 0.00363

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "27.25"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "pfv",
          "access_type": "range",
          "possible_keys": [
            "PRIMARY",
            "fl",
            "variant_id",
            "lang_code",
            "product_id",
            "fpl",
            "idx_product_feature_variant_id"
          ],
          "key": "product_id",
          "used_key_parts": [
            "product_id"
          ],
          "key_length": "3",
          "rows_examined_per_scan": 40,
          "rows_produced_per_join": 2,
          "filtered": "6.76",
          "index_condition": "(`cscartdb`.`pfv`.`product_id` in (20840,20730,20720,20748,20970,20760,14099,20712,20713,15481,16046,16055,17412,20954,20743,20765,16100,16036,16037,62954,20953,16098,16035,57917,57934,14136,14111,16045,57946,57947,14116,57916,21010))",
          "cost_info": {
            "read_cost": "25.99",
            "eval_cost": "0.27",
            "prefix_cost": "26.26",
            "data_read_per_join": "2K"
          },
          "used_columns": [
            "feature_id",
            "product_id",
            "variant_id",
            "lang_code"
          ],
          "attached_condition": "((`cscartdb`.`pfv`.`feature_id` in (1482,265,259,258,289,1207,288,287,1466,1461,266,271)) and (`cscartdb`.`pfv`.`lang_code` = 'en'))"
        }
      },
      {
        "table": {
          "table_name": "fv",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY",
            "feature_id"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id"
          ],
          "key_length": "3",
          "ref": [
            "cscartdb.pfv.variant_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 0,
          "filtered": "5.00",
          "cost_info": {
            "read_cost": "0.68",
            "eval_cost": "0.01",
            "prefix_cost": "27.21",
            "data_read_per_join": "157"
          },
          "used_columns": [
            "variant_id",
            "feature_id",
            "position"
          ],
          "attached_condition": "(`cscartdb`.`fv`.`feature_id` = `cscartdb`.`pfv`.`feature_id`)"
        }
      },
      {
        "table": {
          "table_name": "fvd",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "variant_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "cscartdb.pfv.variant_id",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 0,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "0.03",
            "eval_cost": "0.01",
            "prefix_cost": "27.25",
            "data_read_per_join": "418"
          },
          "used_columns": [
            "variant_id",
            "variant",
            "lang_code"
          ]
        }
      }
    ]
  }
}