Get the Operator Profile in use from the top-right menu:

Then under (Guest) -> Administration -> Operator Logins -> Profiles, select the Super Administrator (or profile you found in the previous step). Click on it and then click Edit.
Scroll to the bottom and find the Language selector, which you can change from 'Auto-detect' to your preferred language:

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Herman Robers
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If you have urgent issues, always contact your Aruba partner, distributor, or Aruba TAC Support. Check
https://www.arubanetworks.com/support-services/contact-support/ for how to contact Aruba TAC. Any opinions expressed here are solely my own and not necessarily that of Hewlett Packard Enterprise or Aruba Networks.
In case your problem is solved, please invest the time to post a follow-up with the information on how you solved it. Others can benefit from that.
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