Hello,
Welcome to Microsoft Community and appreciate your time taken for sharing detailed information. I understand that Office Android App Language Proofing. I could share with you some of my thoughts on this issue.
I'd like to ask what type of phone you have? Usually this is how we change the proofreading language. In Word on your Android phone, tap Edit
at the top of your screen, and then tap Proofing and Language under Review.
In Word on your Android tablet go to the Review tab and you can select your proofing language from the ribbon.
And you could refer to this link for details: Change the language Office uses in its menus and proofing tools (microsoft.com)
Feel free to post back if you need any further assistance.
Best Regard,
Kevin | Microsoft Community Support Specialist
*Beware of scammers posting fake support numbers here."
*Kindly Mark and Vote this reply if it helps, as it will be beneficial to more community members reading here.
*If your problem is not solved, you could reply to the post again and we would continue to provide technical support for you.