Starting Windows 10 Build 1803 adding a new input language to Windows 10 is not an easy task. Adding it via settings may cause two issues: adding an additional en-US language, which is most likely not required in Australia, and arbitrary changing the application interface to the wrong language.
This PowerShell scripts adds new languages correctly without affecting the rest of OS (in my case I need 3 languages for my day to day business, English (AU), German and Russian).
Note that this code will remove all previous language settings.
$1=New-WinUserLanguageList en-AU $1.Add("de-DE") $1.Add("ru-RU") Set-WinUserLanguageList $1