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 (
    23660, 23659, 23403, 23405, 23404, 23654, 
    23653, 23391, 23658, 23392, 23394, 
    23400, 23398, 23652, 23656, 23657, 
    23402, 23401
  ) 
  AND pfv.product_id IN (
    35929, 35925, 32703, 32706, 32704, 35917, 
    35916, 33081, 35921, 32679, 32683, 
    32696, 32691, 35912, 35919, 35920, 
    32700, 33102
  ) 
  AND pfv.lang_code = 'en'

Query time 0.02624

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": "fl",
          "key_length": "9",
          "used_key_parts": ["feature_id", "lang_code"],
          "rowid_filter": {
            "range": {
              "key": "product_id",
              "used_key_parts": ["product_id"]
            },
            "rows": 97,
            "selectivity_pct": 0.061313241
          },
          "rows": 72,
          "filtered": 0.061313242,
          "index_condition": "pfv.feature_id in (23660,23659,23403,23405,23404,23654,23653,23391,23658,23392,23394,23400,23398,23652,23656,23657,23402,23401) and pfv.lang_code = 'en'",
          "attached_condition": "pfv.product_id in (35929,35925,32703,32706,32704,35917,35916,33081,35921,32679,32683,32696,32691,35912,35919,35920,32700,33102)"
        }
      },
      {
        "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'"
        }
      }
    ]
  }
}