If you find that you no longer have the Character Picker (that's the popup menu with accented versions of the key you are holding down), I've seen two fixes that sometimes work:
+Use the plus and add buttons in system preferences/keyboard/input sources to add another keyboard like French or Spanish to your list of active keyboard layouts.
+Go to system preferences/keyboard and toggle the key repeat rate to Off and then on again.
Reboot afterwards.
+Use the plus and add buttons in system preferences/keyboard/input sources to add another keyboard like French or Spanish to your list of active keyboard layouts.
+Go to system preferences/keyboard and toggle the key repeat rate to Off and then on again.
Reboot afterwards.