Microsoft Graph - Filtering with umlaut and other Unicode characters

Question

How can I formulate a query for Microsoft Graph /myOrganization/users OData that contains non-English characters like Germanic Umlauts?

Example: I have a user in my tenant named "Thomas Müller". If i ask

https://graph.microsoft.com/v1.0/myOrganization/users?$filter=startswith(surname,'mu')

I get

 "value": [ { "displayName": "Thomas Müller", "givenName": "Thomas ", "surname": "Müller" } ] // Result truncated for brevity 

but if i'm looking

https://graph.microsoft.com/v1.0/myOrganization/users?$filter=startswith(surname,'mü')

I get

"value": []