+
С долгими гласными вообще получается что-то ужасное:
Äänekoski -> Aeaenekoski?
Или:
Räikkönen -> Raeikkoenen?
Вообще, насколько я помню, передача
ä сочетанием
ae (и т.д.) допускается в языках, где эти звуки образовались в результате умлаута, т.е. в германских языках.
Из Вики:
The letter Ä occurs in the Finnish, Estonian, Swedish and Slovak alphabets, where it represents a vowel sound. In Finnish this is always [æ]; in Estonian regional variation allows for either [æ] and [ɛ]. Note that unlike the A umlaut (see below), the letter Ä cannot be written as "ae". In Finnish, for example, there is a large number of such minimal pairs, e.g. hän ~ haen "s/he ~ I seek".
In Finnish, its name is Ä [æː], not "A with two dots", since Ä represents an unrelated phoneme to A. It is considered a distinct letter separate from A, and placed in the Finnish alphabet after Z and Å but before Ö.
http://en.wikipedia.org/wiki/%C3%84
The letter Ö occurs in the Finnish, Karelian, Estonian, Hungarian, Azeri, Turkish and Crimean Tatar alphabets, where it represents the vowel sound [ø]. Its name in Finnish and Estonian is Öö [øː], not "O with two dots", since /ö/ is not considered a "variant" of the phoneme /o/, but a distinct phoneme.
Note that unlike the O-umlaut (see below), the letter Ö cannot be written as "oe". Minimal pairs exist between 'ö' and 'oe' (and also with 'oo', 'öö' and 'öe'). Consider Finnish eläinkö "animal?" (interrogative) vs. eläinkoe "animal test", or Finnish töissä "at work", toissa "before last" (cf. Germanic umlaut). In the case the character Ö is unavailable, O is substituted and context is relied upon for inference of the intended meaning.
It is collated as an independent letter, usually by placing it at the end of the alphabet. It is the last letter in the Finnish alphabet, after Z, Å and Ä, thus fulfilling the place of "omega", for example in the Finnish expression aasta ööhön "from A to Z".
http://en.wikipedia.org/wiki/%C3%96