I have installed WPML to my Marketpress and installed Russian language.
One of the things I made was translating the URL's to make it more SEO.
But I have found that I cannt use PayPal in this case.
The problem lies with the Plugins-Gatewas/paypal-express.php (I have not yet checked others...)
Lines: 69-70 should look like this:
$this->returnURL = urlencode(mp_checkout_step_url('confirm-checkout')); $this->cancelURL = urlencode(mp_checkout_step_url('checkout')) . "?cancel=1";
What I added is urlencode(); to the URL sent to paypal.
Please add this to the next release to it will not break my code.