TapNoiseIn many Mac text fields, holding a letter opens an accent menu. Choose the accented form with its displayed number or the pointer. Availability depends on the app, letter and input source.
Try the accent menu first
Open TextEdit and hold a vowel such as A. If the menu appears, select the form you need and continue typing. If it does not, try the app’s text-entry documentation before changing system-wide settings.
A held key does not always repeat the character: the accent menu is one reason. Code editors and terminal applications may use different behaviour from ordinary document fields.
Use the current layout’s combinations
Show Keyboard Viewer and hold Option or Shift to reveal alternate characters. Some accent keys start a sequence: you enter the accent first, then the letter it should modify.
The correct combination depends on the selected input source. Avoid copying a shortcut for a US layout and assuming it will match a different regional keyboard.
Make frequent multilingual typing easier
If you regularly write in several languages, add an appropriate input source and keep the Input menu visible. Apple’s ABC Extended layout is another option for Latin-script accents; test the characters you actually use before adopting it.
For an occasional symbol rather than a letter accent, Character Viewer is a simpler route. A sound app changes the audio of the press, not the accent or language produced.