Umlaute/Mutation not working

Hi!

I noticed that I can’t get a good (green) SEO fore some Keywords.
It seems, that it doesn’t recognizes the KWs.

For example “Portr?t”.

I thinkt it might be because of the mutation.
It would be great if this is fixed, because it concerns all german Sites using your plugin ??

Cheers,
J

https://www.ads-software.com/plugins/wordpress-seo/