Dear Alex Ruda
Welcome to the Microsoft Community! We are happy to assist you.
Understanding that you're having trouble setting the default language for Office.
What version of Office do you have? You can open Excel - File - Accounts and provide a screenshot under “Product Information” (if you have an email address or something private, encode it and upload it).
You can try to delete the English language pack, quit the Office application, and then download it from Language Accessory Pack for Microsoft 365 - Microsoft Support to reinstall the English language pack.
If your organization has Office installed on your computer, contact IT to install any language packs.
If the installation fails, at what point in the installation process will you see an error message? You can attempt to perform an online repair of the Office installation, as described in the Knowledge Base article: Repair an Office application - Microsoft Support
Thank you for your understanding and patience. We would appreciate it if you could come back to us.
Jennie | Microsoft Community Support Specialist