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 (
    20322, 23646, 24313, 24310, 23726, 19675, 
    19981, 22102, 24546, 24299, 24312, 
    22632, 22627, 19984, 24309, 24501
  ) 
  AND pfv.product_id IN (
    4287, 35690, 42187, 42182, 36522, 6481, 
    5599, 24715, 44940, 42168, 42186, 27078, 
    27076, 5596, 42181, 44599
  ) 
  AND pfv.lang_code = 'en'

Query time 0.03502

JSON explain

{
  "query_block": {
    "select_id": 1,
    "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": "PRIMARY",
          "key_length": "6",
          "used_key_parts": ["feature_id", "product_id"],
          "rows": 282,
          "filtered": 0.016709697,
          "attached_condition": "pfv.feature_id in (20322,23646,24313,24310,23726,19675,19981,22102,24546,24299,24312,22632,22627,19984,24309,24501) and pfv.product_id in (4287,35690,42187,42182,36522,6481,5599,24715,44940,42168,42186,27078,27076,5596,42181,44599) and pfv.lang_code = 'en'",
          "using_index": true
        }
      },
      {
        "table": {
          "table_name": "fv",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY", "feature_id"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["variant_id"],
          "ref": ["dev_db.pfv.variant_id"],
          "rows": 1,
          "filtered": 100,
          "attached_condition": "fv.feature_id = pfv.feature_id"
        }
      },
      {
        "table": {
          "table_name": "fvd",
          "access_type": "eq_ref",
          "possible_keys": ["PRIMARY"],
          "key": "PRIMARY",
          "key_length": "9",
          "used_key_parts": ["variant_id", "lang_code"],
          "ref": ["dev_db.pfv.variant_id", "const"],
          "rows": 1,
          "filtered": 100,
          "index_condition": "fvd.lang_code = 'en'"
        }
      }
    ]
  }
}