agents Gemini Realtime problems with other languages (e.g. German) on agents v1 and 0.x

Hey, I'm trying to replace my openai realtime agent with the google gemini one. For this I've set up the agent via the v1 AgentSession with the model:

model = google.beta.realtime.RealtimeModel(
            model="gemini-2.0-flash-live-001",
            location="europe-west3",
            instructions=instructions,
            voice="Puck",
            modalities=[Modality.AUDIO],
        )

However I can't set the language for the realtime agent. I want it to speak common languages like German, Spanish, English and French. It speaks German but it doesn't work with Umlauts (ö, ü, ..) and it also starts dictating single characters in the middle of the sentence. This happens both on agents v1 and 0.x.

On googles aistudio playground (https://aistudio.google.com/live) this works really well. I also can specifically set the language to German. Is this what's missing here? Or is there an option to set the language for realtime agents? What if the user wants to switch languages during the conversation? In openai realtime this works seamlessly.

Would love to add gemini realtime to my service so any help / fixes would be much appreciated. Thanks! <3