Today I ran into a problem where new Excel documents would open using Arabic as the default language which caused the cells to show in reverse order and the tabs to show incorrect language.
All Office language settings were set to English with no additional languages installed. Additionally all Windows region and language settings also set to US English
Checking Programs and Features showed multiple versions of Office installed in multiple languages.
Uninstalled the Arabic language version but issue still persisted. I Used the Office removal tool which can be downloaded from the link below to removal all Office installations.
Once the tool finished I rebooted the laptop and reinstalled Office 365 and Excel now uses English as default language and displays correctly