As well the feminine form of the common adjective "ambigu" has been "regularized" to place the diaeresis ("tréma" in French) on the pronounced u rather than an on the mute e added for the regular feminine "ambigüe": it also correctly forces the pronunciation of this u, which would otherwise be mute too as an "u" after a "g" is often there only to avoid to read it as a "j" (like in "exergue", "digue" and many terms ending in "-gue(s)" where only the final /g/ is pronounced). Not writing this tréma anywhere would be false. The tradition placed the diaereis on the mute e but it was not clear that it meant pronoucing the "u" before as a vowel.
For terms like "ambigüité" it is also more natural to place it on the "u" (to break the normal "gu" digram which is consonnantal only and have some vocal rendering of the "u" vowel, even if here it would be pronounced more like a short but clearly spelled half-vowel sliding to the next "i", as in "huile" or "lui", but still not like a /w/ as in "oui" /wi/: normal French never pronounces an isolated "u" as /u/ like in English, except where it occurs in the French digram "ou" /u/ which is itself never like an English diphtong; the standard French "u" is pronounced like the German /y/ written as the digram "ue" or as "ü" with its umlaut... which is not a diareasis phonetically; French transforms this "u" /y/ into a gliding semivowel where it immediately precedes another non-mute and non-nasal vowel; but French ortography has no specific letter for this semivowel which remains written "u", or "ü" only where it has to be detached to avoid prononcing it as with normal digrams composed with it) a 2017-07-15 2:32 GMT+02:00 Marcel Schneider via Unicode <unicode@unicode.org> : > On Fri, 7 Jul 2017 16:14:04 +0100 (BST), William_J_G Overington via > Unicode wrote: > > > […] > > > > For example, it mentioned the u diaeresis used in French, though I > learned later that words that have a u diaeresis in French are rather rare. > > > Today, words containing 'u diaeresis' have become more frequent in French, > since last fall (2016) a reformed orthography designed as soon > as in 1990 [1] has become valid (though it is not mandatory [2]). Among > the novelties, it specifies that words like "to disambiguate" have > the diaeresis shifted from the last 'i' of «désambiguïser» to the 'u' of > «désambigüiser». > > Kind regards, > > Marcel > > [1] https://en.wikipedia.org/wiki/Reforms_of_French_orthography#Tr.C3.A9ma > [2] https://en.wikipedia.org/wiki/Reforms_of_French_orthography# > cite_note-6 > >