A better way to set your language is to open up Editor preferences and under Appearance section there will be an option to specify your locale information.
In next major release 4.1.0, this setting will be moved under a new Region & Language category in Editor preferences. Be aware that in 4.0.0 build changing locale only affects currently opened project, so splash screen and project browser will always be in your OS language. We’ve fixed this issue as well in 4.1.0.
Thanks for bringing this to our attention!