Natlang Uses of Diaeresis and Umlaut

Diaeresis (known as tréma in French) and umlaut both employ the same character. But there is a difference of use between diaeresis and umlaut. Letters with umlaut stand for completely different sounds than their non-accented counterparts. For example in Swedish Oo represents /u/ while Öö represents /ø/. Diaeresis on the other hand does not change the sound value of a letter, but instead marks that a vowel is not part of a diphthong or digraph. Both are also known under the general name trema.
The diaeresis and umlaut characters have different origins. Diaeresis was borrowed from the Greek alphabet,[1] while umlaut began as a small e placed on top of Aa, Oo or Uu. This e then later evolved into the same shape as diaeresis.[2]

Diaeresis/Umlaut in Unicode

Precomposed Letters with Diaeresis/Umlaut

¨

◌̈

Ä

ä

Ǟ

ǟ

Ë

ë

Ḧ

ḧ

Ï

ï

Ḯ

U+00A8

U+0308

U+00C4

U+00E4

U+01DE

U+01DF

U+00CB

U+00EB

U+1E26

U+1E27

U+00CF

​ U+00EF

U+1E2E

Diaeresis

Combining Diaeresis

Latin Capital Letter A With Diaeresis

Latin Small Letter A With Diaeresis

Latin Capital Letter A With Diaeresis And Macron

Latin Small Letter A With Diaeresis And Macron

Latin Capital Letter E With Diaeresis

Latin Small Letter E With Diaeresis

Latin Capital Letter H With Diaeresis

Latin Small Letter H With Diaeresis

Latin Capital Letter I With Diaeresis

Latin Small Letter I With Diaeresis

Latin Capital Letter I With Diaeresis And Acute

ḯ

Ö

ö

Ȫ

ȫ

Ṏ

ṏ

ẗ

Ü

ü

Ǖ

ǖ

Ǘ

U+1E2F

U+00D6

U+00F6

​ U+022A

U+022B

U+1E4E

U+1E4F

U+1E97

U+00DC

​ U+00FC

U+01D5

U+01D6

U+01D7

Latin Small Letter I With Diaeresis And Acute

​ Latin Capital Letter O With Diaeresis

Latin Small Letter O With Diaeresis

​ Latin Capital Letter O With Diaeresis And Macron

Latin Small Letter O With Diaeresis And Macron

Latin Capital Letter O With Tilde And Diaeresis

Latin Small Letter O With Tilde And Diaeresis

Latin Small Letter T With Diaeresis

Latin Capital Letter U With Diaeresis

Latin Small Letter U With Diaeresis

Latin Capital Letter U With Diaeresis And Macron

Latin Small Letter U With Diaeresis And Macron

​ Latin Capital Letter U With Diaeresis And Acute

ǘ

Ǚ

ǚ

Ǜ

ǜ

Ṻ

ṻ

Ẅ

ẅ

Ẍ

ẍ

Ÿ

ÿ

U+01D8

U+01D9

U+01DA

U+01DB

U+01DC

U+1E7A

U+1E7B

U+1E84

U+1E85

U+1E8C

U+1E8D

U+0178

U+00FF

Latin Small Letter U With Diaeresis And Acute

Latin Capital Letter U With Diaeresis And Caron

Latin Small Letter U With Diaeresis And Caron

Latin Capital Letter U With Diaeresis And Grave

Latin Small Letter U With Diaeresis And Grave

Latin Capital Letter U With Macron And Diaeresis

Latin Small Letter U With Macron And Diaeresis

Latin Capital Letter W With Diaeresis

Latin Small Letter W With Diaeresis

Latin Capital Letter X With Diaeresis

Latin Small Letter X With Diaeresis

Latin Capital Letter Y With Diaeresis

Latin Small Letter Y With Diaeresis

Natlang Examples

Uses of Diaeresis or Umlaut

Usage	Language	Letters	Notes
Front version of back vowel (this includes Ää even though its unaccented version is not a back vowel in all of these languages)	Estonian	Ää /æ/, Öö /ø/, Üü /y/
	Finnish	Ää /æ/, Öö /ø/	Usage borrowed from Swedish.
	Livonian	Ää /æ/, Ǟǟ /æː/
	Hungarian	Öö /ø/, Üü /y/
	Slovak	Ää /æ~ɛ/	/æ/ is archaic or dialectal pronunciation.[3]
	Swedish	Ää /ɛ/, Öö /ø/, Üü /y/	The umlaut evolved from the letter e in the digraphs ae[4] and oe[5]. Üü is not really a part of the Swedish alphabet, but is used in some loanwords and in many surnames.
Hiatus	Catalan	Ïï /i/, Üü /u/	Diaeresis on an Ii or Uu following another vowel marks that the two vowels are in different syllables. Without diaresis, the Ii or Uu would stand for a semivowel.[6]
	French	Ëë, Ïï, Üü, Ÿÿ
Non-silent vowel	Catalan	Üü /w/	Diaresis on an Uu that is between Gg or Qq and a front vowel marks that this letter stands for /w/. Otherwise it would be a part of the digraph Gu gu /g/ or Qu qu /k/ that is used before front vowels.[7]
Raised vowel	Hungarian	Ëë /e/	Unaccented Ee stands for /ɛ/. Ëë is not really a part of the Hungarian alphabet however; it is used when writing down spoken or sung language in a dialect that has this phoneme.