Does this have to do with the Language and/or date/time format?
If so, I can confirm that HEAT will automatically select the language based on related settings on your computer. If HEAT is displaying/defaulting to English US, it is caused by a mis-configuration on the computer (which is what IE on Windows or Safari on Mac uses) or web browser settings Chrome/Firefox etc. Chrome/Firefox seem to install with English US as the default language in my experience.
To directly answer your question: I have found no way to set the default locale for all users....perhaps because of what I said above (it's designed to choose it automatically).
I was shown a case on an Android Mobile device where the option to change the Locale in Self Service was there, but it didn't hold its setting.
Luckily we don't officially support such devices, but it is a sad situation.
This didn't make a difference for one of our clients. Still got US English.
Maybe it store in some tables? If we know the table and column, we can create SQL script to update the default locale for all employees.
As at version 2018, it is set / saved in a cookie (after browser locale detection as already described in this thread).
Very few of our users have correct locale settings - we haven’t managed to control this where we could, and we have many customers beyond our control who would be prone to being affected by this.
it would be a very small step for Ivanti to use the Employee configuration to pre-seed the desired locale. Anonymous users would still be caught out, though.
If you run on-prem, you can muck around with this.
See my comments at the bottom of DOC-53519.