Permalink not working for translations

Hi all,
I’ve got a bilingual site.
English, is the default language and permalink treats it just fine.
However, when I add a Greek translation to any page/post (I’m using WPML for translations) permalink tries to fill the URL with Greek characters. This is causing me all sorts of problems as:
a) URLs don’t work and
b) URLs change every time I decide to edit Greek posts.

Currently, I’m manually editing the URL before publishing however, I really dislike this solution.

I’m hugely concerned that my editors will at some point forget to do this.

Can you please advice?

My suggestion: Is there any way of defaulting the URL to it’s English default URL plus a prefix OR just forcing users to edit their own URL?

Any thought would be highly appreciated!
Many thanks in advance