Hello @Steinkrug, Michelle
Thanks for using Microsoft Q&A platform. I think you are mentioning SSML for en-US-JennyMultilingualNeural.
Please check on this guidance - https://learn.microsoft.com/en-us/azure/cognitive-services/speech-service/speech-synthesis-markup?tabs=csharp#adjust-speaking-languages
This is how to custom lexicon - https://learn.microsoft.com/en-us/azure/cognitive-services/speech-service/speech-synthesis-markup?tabs=csharp#use-custom-lexicon-to-improve-pronunciation
I hope this helps, please let me know if you have any question when you have a try.
Regards,
Yutong
-Please kindly accept the answer if you feel helpful to support the community, thanks a lot.