I don't know about the other languages, but we use them in spanish, and since they're used to point out which syllable is the "strongest" in one word, so pointing out two would be wrong.
Like the word : préféré (favorite), in French, accent in a word are only used for the pronunciation, for the "sound", well I can't really explain with a keybord but, to sum it up "e,é,è" have a different intonation in the word and it is also used for conjugation when it's at the end of the word.
In French and German (and probably some other languages) letters that have an accent or umlaut are a different letter than without one and the accent changes the sound of the letter.
.
;)
Bitchés
Fuckér
So fancy.