A family of Microsoft word processing software products for creating web, email, and print documents.
Are you sure you're using a key for a character that has diacritics available? Please provide specific examples.
By and large, alphanumeric characters do not repeat in Word... Only certain symbols such as <spacebar>, ➖ & 〓 repeat. However, repeat delay & rate for those characters is controlled by > System Preferences - Keyboard. Word does not regulate that.
If you continue to have a problem be certain to specify the Version information which you can obtain from Word> About Word in the main menu. Behaviors can vary depending on that information. You did not include that in your original message & posting as an Office Product of Unknown/other gives nothing to go on. Also, it's good to indicate your version of macOS.