Vowels

• In Albanian, Tagalog, and Kashubian, ⟨ë⟩ represents a schwa [ə].
• In Aymara, a double dot is used on ⟨ä⟩ ⟨ï⟩ ⟨ü⟩ for vowel length.
• In the Basque dialect of Soule, ⟨ü⟩ represents [y]
• In the DMG romanization of Tunisian Arabic, ⟨ä⟩, ⟨ö⟩, ⟨ṏ⟩, ⟨ü⟩, and ⟨ṻ⟩ represent [æ], [œ], [œ̃], [y], and [y:].
• In Ligurian official orthography, ⟨ö⟩ is used to represent the sound [oː].
• In Māori, a diaeresis (e.g. Mäori) was often used on computers in the past instead of the macron to indicate long vowels, as the diaeresis was relatively easy to produce on many systems, and the macron difficult or impossible.^[4][5]
• In Seneca, ⟨ë⟩ ⟨ö⟩ are nasal vowels, though ⟨ä⟩ is [ɛ], as in German umlaut.
• In Vurës (Vanuatu), ⟨ë⟩ and ⟨ö⟩ encode respectively [œ] and [ø].
• In the Pahawh Hmong script, a double dot is used as one of several tone marks.
• The double dot was used in the early Cyrillic alphabet, which was used to write Old Church Slavonic. The modern Cyrillic Belarusian and Russian alphabets include the letter ⟨ё⟩ (yo), although replacing it with the letter ⟨е⟩ without the diacritic is allowed in Russian.
• Since the 1870s, ⟨Ї⟩, ⟨ї⟩ (Cyrillic letter yi) has been used in the Ukrainian alphabet for iotated [ji]; plain і is not iotated [i]. In Udmurt, ӥ is used for uniotated [i], with и for iotated [ji].
• The form ⟨ÿ⟩ is common in Dutch handwriting and also occasionally used in printed text – but is a form of the digraph "ij" rather than a modification of the letter ⟨y⟩.
• Komi and Udmurt use ⟨Ӧ⟩ (a Cyrillic O with two dots) for [ə].
• The Swedish, Finnish and Estonian languages use ⟨Ä⟩ and ⟨Ö⟩ to represent [æ] and [ø]
• In the languages of J.R.R. Tolkien's Middle-Earth novels, a diaeresis is used to separate vowels belonging to different syllables (e.g. in Eärendil) and on final e to mark it as not a schwa (e.g. in Manwë, Aulë, Oromë, etc.). (There is no schwa in these languages but Tolkien wanted to make sure that readers wouldn't mistakenly pronounce one when speaking the names aloud.)

Consonants

Jacaltec (a Mayan language) and Malagasy are among the very few languages with a double dot on the letter "n"; in both, n̈ is the velar nasal [ŋ].

In Udmurt, a double dot is also used with the consonant letters ӝ [dʒ] (from ж [ʒ]), ӟ [dʑ] (from з [z] ~ [ʑ]) and ӵ [tʃ] (from ч [tɕ]).

When distinction is important, Ḧ and ẍ are used for representing [ħ] and [ɣ] in the Kurdish Kurmanji alphabet (which are otherwise represented by "h" and "x"). These sounds are borrowed from Arabic.

Ẅ and ÿ: Ÿ is generally a vowel, but it is used as the (semi-vowel) consonant [ɰ] (a [w] without the use of the lips) in Tlingit. This sound is also found in Coast Tsimshian, where it is written ẅ.

A number of languages in Vanuatu use double dots on consonants, to represent linguolabial (or "apicolabial") phonemes in their orthography. Thus Araki contrasts bilabial p [p] with linguolabial p̈ [t̼]; bilabial m [m] with linguolabial m̈ [n̼]; and bilabial v [β] with linguolabial v̈ [ð̼].

Seneca uses ⟨s̈⟩ for [ʃ].

In Arabic the letter ẗ is used in the ISO 233 transliteration for the tāʾ marbūṭah [ة], used to mark feminine gender in nouns and adjectives.

Syriac uses a two dots above a letter, called Siyame, to indicate that the word should be understood as plural. For instance, ܒܝܬܐ (bayta) means "house", while ܒܝ̈ܬܐ (bayte) means "houses". The sign is used especially when no vowel marks are present, which could differentiate between the two forms. Although the origin of the Siyame is different from that of the diaeresis sign, in modern computer systems both are represented by the same Unicode character. This, however, often leads to wrong rendering of the Syriac text.

The N'Ko script, used to write the Mandé languages of West Africa uses a two-dot diacritic (among others) to represent non-native sounds. The dots are slightly larger than those used for diaeresis or umlaut.

Diacritic underneath

The IPA specifies a "subscript umlaut", for example Hindi [kʊm̤ar] "potter";^[3]: 25 the ALA-LC romanization system provides for its use and is one of the main schemes to romanize Persian (for example, rendering ⟨ض⟩ as ⟨z̤⟩). The notation was used to write some Asian languages in Latin script, for example Red Karen.

Apple MacOS, iOS

iOS provides accented letters through press-and-hold on most European Latin-script keyboards, including English. Some keyboard layouts feature combining-accent keys that can add accents to any appropriate letter. A letter with double dots can be produced by pressing ⌥ Option+U, then the letter. This works on English and other keyboards and is documented further in the supplied manuals.^[8]

Google ChromeOS

For ChromeOS with US-International keyboard setting, the combination is "+(letter).^[9] For ChromeOS with UK extended setting, use AltGr⇧ Shift2, release, then the letter. Alternatively, the Unicode codepoint may be entered directly, using Ctrl+⇧ Shift+u, release, then the four-digit code, then ↵ Enter or Space.^[10]

Linux

In some Linux desktop environments a letter with double dots can be produced by pressing AltGr⇧ Shift:, then the letter. When the system has a compose key, the same procedure as that described at X-Windows (below) may be used.

Microsoft Windows

AZERTY and QZERTY keyboards (as used in much of Europe) include precomposed characters (accented letters) as standard and these are fully supported by Microsoft Windows, typically accessed using the AltGr key.

For users with a US keyboard layout, Windows includes a setting "US International", which supports creation of accented letters by changing the function of some keys into dead keys. If the user enters ", nothing will appear on screen, until the user types another character, after which the characters will be merged if possible, or added independently at once if not. Otherwise, the desired character may be generated using the Alt table above.

For users in the United Kingdom and Ireland with QWERTY keyboards, Windows has an "Extended" setting such that an accented letter can be created using AltGr2 then the base letter.

When using Microsoft Word or Outlook, a letter with double dots can be produced by pressing Ctrl⇧ Shift: and then the letter.

On Microsoft Windows keyboard layouts that do not have double dotted characters, one may use Windows Alt keycodes. Double dots are then entered by pressing the left Alt key, and entering the full decimal value of the character's position in the Windows code page on the numeric keypad, provided that the compatible code page is used as a system code page. One can also use numbers from Code page 850; these are used without a leading 0.

X Window System

X-based systems with a Compose key set in the system can usually insert characters with double dots by typing Compose, quotedbl (i.e. ") followed by the letter. Compose+⇧ Shift, letter may also work, depending on the system's set-up. However, most modern UNIX-like systems also accept the sequence Compose+⇧ Shift+U to initiate the direct input of a Unicode value. Thus, typing Compose+⇧ Shift+U, 00F6, finishing with Space or ↵ Enter, will insert ö into the document.

Dedicated keys

The German keyboard has dedicated keys for ü ö ä. Scandinavian and Turkish keyboards have dedicated keys for their respective language-specific letters, including ö for Swedish, Finnish, and Icelandic, and both ö and ü for Turkish. French and Belgian AZERTY keyboards have a dead key which adds a circumflex (if without Shift) or a diaeresis/umlaut (if with Shift) to the letter key immediately following (for instance Shift-^ followed by e gives ë).

Other scripts

For non-Latin scripts, Greek and Russian use press-and-hold for double-dot diacritics on only a few characters. The Greek keyboard has dialytica and dialytica–tonos variants for upsilon and iota (ϋ ΰ ϊ ΐ), but not for ε ο α η ω, following modern monotonic usage. Russian keyboards feature separate keys for е and ё.