UserAgent: Mozilla/5.0 (X11; CrOS x86_64 10323.67.5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/65.0.3325.209 Safari/537.36
Platform: 10323.67.5 (Official Build) stable-channel eve

Steps to reproduce the problem:
1. Enable the onscreen keyboard using accessibility settings.
2. Ensure the system has US English as the only language in all the places where that can be set.
3. Open the onscreen keyboard and enable voice typing by clicking the microphone button.
4. Try to dictate the following phrase: I would like to test this behaviour.

What is the expected behavior?
It types "I would like to test this behavior".

What went wrong?
It types "I would like to test this behaviour". That is UK spelling. This also goes a rhyme with words like optimisation, vectorisation, etc where the us spelling has a z and the UK spelling has an s.

Did this work before? N/A 

Chrome version: 65.0.3325.209  Channel: stable
OS Version: 10323.67.5
Flash Version: