PARAM_XXX does not accept Greek characters

Hello,
and thank you for the nice plugin.

I am trying to use it to produce a feed for Glami.gr, and followed your instructions here: https://adtribes.io/how-to-add-zbozi-cz-and-heureka-cz-params-to-xml-feed/

The problem is that in “PARAM_Anythingyouwant”, when I replace “Anythingyouwant” with Greek characters and try to save, I get the following error:

Sorry, when creating new custom fields only letters are allowed (so no white spaces, numbers or any other character are allowed).

I have tested with latin characters and the output format is correct

<PARAM>
<PARAM_NAME>material</PARAM_NAME>
<VAL>Συνθετικό</VAL>
</PARAM>

But Glami.gr wants “υλικό φόδρας”, or at least “υλικό” (no space) instead of “material”.

Is there any solution to this?