WPML & callbacks

We noticed that some payment notifications were not being handled correctly by the Paytrail for Woocommerce plugin. We are using WPML and found that the payment notifications were being sent to our server using this URL:
/?lang=en/paytrail/callback/index&checkout-account=xxxx…
The added lang parameter in the beginning prevented the callback from being handled correctly by the plugin.

The plugin seems to use home_url() when constructing the callback urls and WPML also hooks into the ‘home_url‘ filter, adding the language parameter if the current language differs from the site’s default language.

We can fix this temporarily by adding our own custom filter to ‘home_url’ in order to override WPML’s modifications, but this should probably be handled internally by the Paytrail for Woocommerce plugin.