Hello
On a computer (not smartphone or tablet), go to www.outlook.com , then click on the gear icon on the upper right to launch Settings. Then use the screenshot below to guide you, so you know where to click to change the language back.
I would suggest that you also go through the following list of things to do, as it sounds like your account might have been compromised.
First, go to https://www.outlook.com and sign in.
Click the gear icon in the top right corner to open Settings.
Under Mail, review the following areas:
Rules
If any rules are listed, delete all of them.
Conditional formatting
If anything is set up there, delete it.
Forwarding and IMAP
If you see any entries or settings you did not create, remove them.
After that, exit Settings and return to outlook.com.
Open the To Do section by clicking the blue checkmark icon on the left side. Delete anything there that was not created by you.
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If you do not find anything suspicious above, go to https://account.live.com.
Under Your info > Sign-in preferences, review all aliases on the account. If you see any alias you do not recognize, remove it.
Next, go to the Devices section of your Microsoft account and remove any devices you do not recognize.
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Please also do the following in Security section
Change your password
Enable two-step verification
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Then go to Security > Manage how I sign in and make sure all contact information belongs to you.
On that same page, scroll down to App passwords and remove any existing app passwords.
Also on the same page, click on Sign out everywhere. This is intended to disconnect any active sessions that may still be connected. Please note that this can take up to 24 hours to fully take effect.
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In addition, this problem can sometimes be caused by a malicious script or infection on one of your devices.
Are you using a Windows computer to check email? Do you use an email app such as Outlook Classic or New Outlook?
If so, please open the app and remove the account from the app settings.
Then go to the Microsoft Safety Scanner download page:
https://learn.microsoft.com/defender-endpoint/safety-scanner-download
Download the 64-bit version, run a full scan, and let me know what the final results say.