How can I change the language of Microsoft Office Online?

Use the browser displayed in that language.

Do as follows;

  1. Login to Microsoft365 portal.
  2. Open OneDrive.
  3. Click [setting] -> [OneDriveの設定].
     -> 
  4. Click [その他の設定] on the left -> [言語設定] on the right.
     -> 
  5. Click [詳細設定を表示].
  6. Choose a language and click [保存].
    ex: English = 英語