Different languages use different rules to put diacritic characters in alphabetical order.
Usually ä is sorted as equal to æ (ash) and ö is sorted as equal to ø (o-slash).
Languages that treat accented letters as variants of the underlying letter usually alphabetize words with such symbols immediately after similar unmarked words. in phone books or in author catalogues in libraries), umlauts are often treated as combinations of the vowel with a suffixed e; Austrian phone books now treat characters with umlauts as separate letters (immediately following the underlying vowel).
For instance, in German where two words differ only by an umlaut, the word without it is sorted first in German dictionaries (e.g. In Spanish, the grapheme ñ is considered a new letter different from n and collated between n and o, as it denotes a different sound from that of a plain n.
Depending on the keyboard layout, which differs amongst countries, it is more or less easy to enter letters with diacritics on computers and typewriters.
Some have their own keys; some are created by first pressing the key with the diacritic mark followed by the letter to place it on.
Modern computer technology was developed mostly in English-speaking countries, so data formats, keyboard layouts, etc.