Category:Phonology
Feature:Vowel Quality Inventories WALS
Name:Average (5-6)
Languages (421):
Conlangs (350):
Esperanto
Klingon
Lojban
Shemspreg
Kamakawi
Terkunan
SASXSEK
Deini
Poswa
Hasu Khomiyo
Khafos
Kelenala
Héhà
Nawe
Kelanian
Naisek
Neo Patwa
Pasgemanh
Isuhuwum
Tseeyo
Bryatesle
Dravean
Jaibi
Rhean
Old Adpihi
Altian
inapo-sakai
Zelsen
Quenya
Sindarin
Velu
Ngeyunh
Yasaro
Jaghri
Toki Pona
Ilvarii
Redspeech
Terpish
Omniglot forum language
Rithande
Adeyan
Ngengenoef
Sathir
Tsolyani
Gogido
Liu
Rejistanian
Latadid
Laadan
Malabas
Tinzirean
Hacherian
Tersales
Gwongbholu
Vitruvian
Depends on how one counts the vowels.  For the most part, y (i), w (u), and r are treated as terminal consonants (diphthongs = VC).
Taruven

6 short vowels

i y ʉ u
e
ɑ

6 long vowels

i:y: ʉ: u:
e:
ɑ:

25 attested diphthongs (grave = falling, acute = rising)

aà aá aì aò aó aỳ eà eá eì eò eỳ ià iá oá oé oì oò uá uì uí yá yè yé yó yú

Geminated consonants can also act as syllable nuclei.

WALS counts this as 6 vowel qualities

Wenedyk
Feayran
Reosian
Kiassan Turasta
Tseltsolian
FIAL
Classical Rossan
Taiwazaiho
Isitya
SIAL
Torete
Moten
Ouxu
Annese

There are 6 vowels (i,ɯ,ɛ,e,ɤ,ɑ).

Alpic
Nejadish
*short:
front       back
/i/         /u/
/e/         /o/
/a/

*long:
front       back
/iː/        /uː/
/eː/        /oː/
/aː/
Rossan
Deata
Wooshe
Reisu
Missa

/a e i o u/, with marginal /ə/.

Itra Kir
Theadish
Classical Magorian
Surang Jumbar
Deiku
Kono Mai
Ishtol
'Yemls
Elesu
Dzuutani

/ɐ̞ e̞ i o̞ u ɨ ɯ*/

*Allophone of /ɨ/

TIAL
Uirian
Ngovasi
Lemohai
Torimish
Waku Front vowels:
/i e a/

Back vowels:
/o u/

Front vowels are centralised following velar or velarised consonants.
Enamyn
IPA: /i ɛ a o ɯ/
X-SAMPA: /i E a o M/
Shuran
Talmit
WNBA
Naeso
Majlang
Plitnakya
Clarnenamerin
Traxvus
Dètren
Sonerha
Ngaru
Avrelang
Rou
Raig
Laroitian
Simpified japanese
Kemba
Fictish
Neo-Fictish
Gac
Emyt
Frimer
Proto-Qephex
Standard Ancaron
Mungitol
Renge-Terra
Qucheanya
Proto-Disu
Lonaane
Wanya
6: i ɘ u ɛ a ɔ
Doline
zadu
Cljek Pikay
Rawang Ata
Antiranto
Kti
Kti has six vowel qualities: /a ɛ i ɔ u ɞ/
Lonmai Luna

basic vowels:/a/,/e/,/i/,/o/,/u/, and /ə/ is used for epenthesis

Dhannuá
Nevotak

short: /a//e//i//o//u/

long: /a:/(written as aa)/i:/(written as ii)/o:~u:/(written as oo)

Renian
UNROUNDED: /i e a/
ROUNDED: /u o/

There are no diphthongs.
Treyll
Kostakan
UNROUNDED: /i e a/
ROUNDED: /u ɔ/

There are no diphthongs.
Kannow
a e ə i ɨ u, long vowels can occur but are marginal and usually resulting from elision or vowel clusters, so I didn't include them -- http://kneequickie.com/kq/Kannow#Vowels
Lhaa: Siri

/i/, /iː/, /y~u/, /yː~uː/, /ɑ/, /ɑː/

Manchu
Tlaymyts
Korpasian
Rammy
Arroe
Proto-Frinthan
Lodeen
Lodeen phonemic vowels are :

/a/ /e/ /i/ /o/ /u/.

A wide range of free allophony might occur depending on the locutor's habits of speaking, like for example, /e/ and /o/ might become /ɛ/ and /ɔ/ in word-final position when followed by a consonant.
yiqa' yiywos

/ɑ/(transcripted as a),/ɛ/(transcripted as æ),/e/(transcripted as e),/i/(transcripted as i),/o/(transcripted as o),/u/(transcripted as u)

toka na musume

/a//e//i//o//u/

gombazi
Orin
Athah
Arano
Town Speech
anotherunnamed
Kaynuryos
Prsänëan
Lup (Simplified)
5 vowel qualities

/a/
/e/
/i/
/o/
/u/
Latha
Ancient Yakim Language
Old Pakhriban
Kobardon
K'u1k'uts'
Tslure Thujekatsoth
Alahithian
a e i o u No dipthongs
Loglan
Kashithes
Kiswona
Okuna
Fasime
Interlingua
Lci
westcontinental Ngyamkyehe language
Pupupulandish
Idhunaic
Tatari Faran
Platapapan
Maja
Doayâu
Q'oligo
Inilt
Northern Lorkan
/a  e    i  o  u /
«a  e   i,é o u,ó»

/ã ẽ ĩ õ ũ/
«ą ę į ǫ ų»
Tengan
Old Zarcosian
Seto ka'palo

normal vowels: /a//e//i//o//u/

reduced vowel: /ɨ/

Thensarian

6

Palethian
Jumban
Shokitin

Shokitin's vowels, while average in number, as unusual in their qualities: both close vowels are unrounded, while both mid vowels are rounded.

Proto-Angelic
Bhadlam
Tizian
Xazik Gohuilim
Madekankomi
G70200
Netagin
Coral Reef language
Levran /i/, /u/, /e/, /o/, /a/
Kuty
Tolvian
Haikyly
Old Nevotak

short vowels: ə - /ə/ i - /i/ u - /u/

long vowels: a - /a:/ e - /e:/ ii - /i:/ o - /o:/ uu - /u:/

clikli dialect
Raxic
Eranai
/a, i, ɯ, e, o/
Ilaini
Laozhea
Glosa
Aingeljã
Haneko
Rireinutire
Phitonic
Guzadinkya
Leopardish III
Sunbyaku
Geulish
Usangtari
Avemuacha
Amqoli
Ronc Tyu
Khulls
Gammidge
Abaru Human Proto-Language
Grapheme IPA
A,a ä
E,e ə
I,i i
O,o o
U,u u
Keihansoukaishi
Telim
Azniar
Oter Tov Svik
Vitran
Taalen
Guezu
Primitive Ayinis
Old Balres
Primitive Averlis
Lohsee
Laucariman
Achiyitqan
Maraxxian
Kaidu
Nuim
NaN
SLMN
Testarossa
Cikap
National Simphonian
Keintra
Old Greedian
Maqacho
Vtayn
Averagelang
Rogel
Savvinic
Leopardish IV
Hy'Bae
Literary Fire
Vrkhazhian
Workinprogressian
Summerlandic
Mira
Proto-Tampoluric
Monophthongs  /a e i o u/
Diphthongs    /ai̯ au̯ ei̯ eu̯ oi̯ ou̯ ui̯/
Kratish
Mirexu
Cheklomino
Temporary1
Alfen
Settamu
Hafojugat Pehapevum (Middle Western)
Jutean
Pach'o
Haotyetpi
Clofabian
Yuzojo
Suiacuili
Opus
Hux Kham
bal'ukbar
/i ɛ a ɔ u ɨ/
Naharqan
Ido
Negric
Arcaicam Esperantom
Mondlango
Lingwa de Planeta
Lioa e Gweu
Pasi
Nattoretan
diSellat
Lingua Franca Nova
Idiom Neutral
Tajju-njo Gwa
Ensurti
Interlingua Antic
Hayaxmi
Uropi
Kotava
Numi
Ganur Lon
Onnasurin
Ussaria
Khan Nilau Khaftim
Gadu Fav
Mayato MKII
Thosk
Lrahran
amman iar
Carrajina
Common Honey
Firen
Firen has a 6-vowel basic system with two phonemic diphthongs and three r-colored vowels.
/i e a ɵ o u/ ⟨i e a ů o u⟩
/ɚ ɑɚ ɔ˞ aɪ aʊ/ ⟨ůṙ aṙ oṙ ai ao⟩
Ilawokou
Urracheg
Diplomatic Shessith
Pejlanrau Khanech Khaftim
Magralgarlu
Sape
Kibaki
Xingish
Lortho
Qrai
Faikari
Interglossa
Ancient Caspian
Nomikan
Gan Dostau
Kiriyow (Creole)
TBD
Average Conlang
a, e, i, o, u
Pandunia
Esperanto 1894
Istokahi
Voksigid
Dunia
Seignuric
Novial
Eldtyric
Laga
Vayardyio
Tadiraki Language
Nylaf
Pandunia (Inflected)
Unish
ExoticLang
Esata
Melfem
Intal
Frater
mundezo
Zdetl
Gavaro
Huttese (fanmade)
Hallon
Dhakhsh
Shalolese
a, e, i, o, u, ə
(a, e, i, o, u, v)

Natlangs (71):
Mandarin
Indonesian
Japanese
Russian
Spanish
Acoma
Arabic (Egyptian)
Ainu
Amele
Apurina
Asmat
Basque
Burushaski
Chamorro
Chukchi
Evenki
Fijian
Georgian
Greek (Modern)
Guarani
Hausa
Hindi
Hixkaryana
Hmong Njua
Ingush
Iraqw
Jakaltek
Ju|'hoan
Kewa
Khoekhoe
Khasi
Kiowa
Kilivila
Kannada
Latvian
Lavukaleve
Lezgian
Lakhota
Luvale
Maori
Mapudungun
Maricopa
Maung
Maybrat
Meithei
Mixtec (Chalcatongo)
Mangarrayi
Ndyuka
Nivkh
Oromo (Harar)
Persian
Rapanui
Slave
Swahili
Tagalog
Tukang Besi
Wari'
Wichi
Warao
Yagua
Yaqui
Yukaghir (Kolyma)
Zulu
Polish
Mundari
Karok
Koyraboro Senni
Nenets
Trumai
Coos (Hanis)
Urubu-Kaapor