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 (
    23318, 21873, 19671, 21173, 20106, 22269, 
    22351, 22930, 20725, 23323, 23324, 
    20722, 23310, 22070, 23707, 19584, 
    21329, 23587
  ) 
  AND pfv.product_id IN (
    32312, 23992, 6521, 2236, 5143, 25245, 
    376, 29732, 3190, 32318, 3195, 32305, 
    813, 36573, 6646, 1973, 35483
  ) 
  AND pfv.lang_code = 'en'

Query time 0.05194

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": 336,
          "filtered": 0.049935829,
          "attached_condition": "pfv.feature_id in (23318,21873,19671,21173,20106,22269,22351,22930,20725,23323,23324,20722,23310,22070,23707,19584,21329,23587) and pfv.product_id in (32312,23992,6521,2236,5143,25245,376,29732,3190,32318,3195,32305,813,36573,6646,1973,35483) 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'"
        }
      }
    ]
  }
}