Diacritics, often loosely called `accents', are the various little dots and squiggles which, in many languages, are written above, below or on top of certain letters of the alphabet to indicate something about their pronunciation. Thus, French has words like été `summer', août `August', ça `that' and père `father'; German has Wörter `words' and tschüss `good-bye'; Spanish has mañana `tomorrow' and ángel `angel'; Norwegian has brød `bread' and frå `from'; Polish has Nza `tear', ^@le `badly' and pica `five'; Turkish has ku^@ `bird' and göz `eye'; Welsh has t^@ `house' and sïo `hiss', and so on. When you are citing a word, a name or a passage from a foreign language which uses diacritics, you should make every effort to reproduce those diacritics faithfully. Fortunately, most word processors can produce at least the commoner diacritics.
You are most likely to need to do this when citing names of persons or places or titles of literary and musical works. The French politician is François Mitterrand, the Spanish golfer is José-María Olazábal, the Polish linguist is Jerzy KuryNowicz, the Turkish national hero is Mustafa Kemal Atatürk, the beleaguered town in the former Yugoslavia is Gora^@de, Wagner's opera is the Götterdämmerung and the French film is Zazie dans le Métro. So far as you can produce them, therefore, these are the forms you should use even when writing in English. But don't overdo it. If an accepted English form exists, use that: write Munich, not München, Montreal, not Montréal, The Magic Flute, not Die Zauberflöte.
In English, diacritics are not normally used, but they occur in three situations. First, many foreign words and phrases have been borrowed into English, and some of these are not yet regarded as fully anglicized. Such forms should be written with their original diacritics, and they should also be written in italics, if possible, to show their foreign status:
Many other such items have become so completely anglicized that they are now usually treated as ordinary English words. Hence, most people now write cafe, rather than café, naive, rather than naïve, and cortege, rather than cortège, and such words are not normally italicized in any case. If you are in doubt about these, you should, as always, consult a good dictionary.
Second, one particular diacritic, the diaeresis (¨), is very occasionally written in English to show that a vowel is to be pronounced separately. A familiar example of this is the name Zoë, but other cases exist. A few people write coöperate, rather than cooperate, and aërate, rather than aerate, but the spellings with the diaeresis are now decidedly old-fashioned and not recommended. Usage varies with the surname Brontë: all the members of this famous family spelled their name with the diaeresis, which should therefore perhaps by retained by the usual rule of respecting the preferences of the owner of a name, but many people nevertheless now write Bronte.
Third, a grave accent (`) is occasionally written over the letter e in the ending -ed to show that it is pronounced as a separate syllable. Thus we write a learnèd scholar or an agèd man to show that learnèd and agèd are each pronounced here as two syllables. Compare I learned French at school and He has aged rapidly, in which learned and aged are pronounced as single syllables.
For convenience, here are the names of the commoner diacritics: