PayPal IPN amount_fee fatal error when decimal separator is not "."

How to reproduce:

• in Admin > Localization > set "," as the decimal separator.
• create a contribution page using PayPal Standard
• using the front-end contribution page, donate an amount that will cause a decimal fee_amount (ex: a 1$  transaction should incur 0.33$ in paypal fees)
• notice that the transactions stays pending, the IPN is never processed.

Looking at the CiviCRM logs, there is this error:

"fee_amount is  not a valid amount: 0.33"

CiviCRM is expecting 0,33 instead of 0.33, but this is information from PayPal, so expecting the data to be localized does not make sense.