Given how well cough the assistant has been able to cope with accents in English (it hasn't very well at all) it will be interesting to see how well this works in practice.
That being said, I feel both G.Assistant, and Alexa both interpret what I'm saying most of the times. In contrast, Siri rarely understands me well. When I set up reminders, 95% of the times Siri fails to comprehend me correctly.
I don't know what they are doing at Apple, but you would think they would have nailed this already (with the millions of Siri capable devices they have sold already).
Happy to hear about more recent tests or counter examples!
(Disclosure: I work at Google, my Google Home tends to get my Canadian English pretty well)