SpeechSynthesisUtterance objects specified with a lang attribute that doesn't have a corresponding Synthesizer on the system will throw an error in MS Edge 44 (non-chromium edge). Other browsers will find the most appropriate synthesizer to use. For example in the Orator demo the lang is set to "en-CA". In my Windows 10 VM, MS Edge 44 only has synthesizers that support "en-US". If the lang is even specified as "en" it will still throw an error. This seems like a bug in the browser and it's unlikely it'll get fixed now that they've moved to a new version of Edge that is based off of Chromium.