Afrikaans: agtien (af) , agttien (af)
Albanian: tetëmbëdhjetë (sq)
American Sign Language:
Amharic: አስራ ስምንት ( ʾäsra səmnət )
Arabic: ثَمَانِيَةَ عَشَرَ ( ṯamāniyata ʕašara )
Egyptian Arabic: تمنتاشر ( tamantāšar )
Aramaic:
Hebrew: תמנעסר m ( tmāna‘sar ) , תמנעסרא f ( tmāna‘esrē )
Syriac: ܬܡܢܥܣܪ m ( tmāna‘sar ) , ܬܡܢܥܣܪܐ f ( tmāna‘esrē )
Armenian: տասնութ (hy) ( tasnutʿ )
Old Armenian: ութեւտասն ( utʿewtasn )
Asturian: dieciocho (ast)
Aymara: tunka kimsaqallquni
Azerbaijani: on səkkiz (az)
Bashkir: ун һигеҙ ( un higeð )
Basque: hemezortzi (eu) , hamazortzi (eu)
Belarusian: васямна́ццаць ( vasjamnáccacʹ ) , васемна́ццаць ( vasjemnáccacʹ )
Bengali: আঠারো (bn) ( aṭharō ) (numeral: ১৮ )
Bikol Central: kagwalo
Breton: triwec'h (br)
Brunei Malay: lapan balas
Bulgarian: осемна́десет ( osemnádeset ) , осемна́йсет ( osemnájset )
Burmese: ဆယ့်ရှစ် ( hcai.hrac ) (numeral: ၁၈ )
Buryat: арбан найман ( arban najman )
Catalan: divuit (ca)
Valencian: díhuit (ca)
Cebuano: napulog walo
Central Sierra Miwok: naˀá·ča- káw·inṭa-ˀ hej·i-ˀ
Chechen: берхӏитта ( berhitta )
Cherokee: ᏁᎳᏚ ( neladu )
Chichewa: khumi n'zisanu n'zitatu
Chinese:
Cantonese: 十八 ( sap6 baat3 )
Hakka: 十八 ( sṳ̍p-pat )
Mandarin: 十八 (zh) ( shíbā )
Chuvash: вунсаккӑр ( vuns̬akkăr ) , вунсаккăр ( vuns̬akkăr ) , вунсакăр ( vuns̬akăr )
Classical Nahuatl: caxtōlli omēyi
Cree: ᐊᔨᓇᓀᐅᐧᓴᑊ ( ayinaneoysap )
Czech: osmnáct (cs)
Danish: atten (da)
Dena'ina: łtaqul'i beq'di
Dhivehi: އަށާރަ ( aṣāra )
Dutch: achttien (nl) f
Dzongkha: བཅོ་བརྒྱད ( bco brgyad )
Esperanto: dek ok
Estonian: kaheksateist (et)
Faroese: átjan
Fijian: tini ka walu
Finnish: kahdeksantoista (fi)
French: dix-huit (fr) m
Galician: dezaoito (gl)
Georgian: თვრამეტი (ka) ( tvrameṭi )
German: achtzehn (de)
Greek: δεκαοκτώ (el) ( dekaoktó )
Ancient: ὀκτωκαίδεκα ( oktōkaídeka ) , ιη΄ ( numeral )
Greenlandic: arfersaneq-pingasut (kl)
Gujarati: અઢાર (gu) ( aḍhār )
Haitian Creole: dizuit
Hawaiian: ʻumikūmāwalu
Hebrew: שְׁמוֹנֶה־עֶשְׂרֵה f ( shmone-esre ) ( used in counting ) , שְׁמוֹנָה־עָשָׂר m ( shmona-asar )
Hindi: अठारह (hi) ( aṭhārah )
Hopi: pakwt niikyang nanalt siikya’ta
Hungarian: tizennyolc (hu)
Hunsrik: achtzen
Icelandic: átján (is) , áttján ( archaic )
Ido: dek ed ok (io)
Inari Sami: käävcinubáloh
Indonesian: delapan belas (id)
Ingrian: kaheksantoist
Interlingua: dece-octo
Irish: ocht déag
Italian: diciotto (it)
Japanese: 十八 (ja) ( jūhachi )
Kannada: ಹದಿನೆಂಟು (kn) ( hadineṇṭu )
Kazakh: он сегіз (kk) ( on segız )
Khmer: ដប់ប្រាំបី ( dop pram bei ) (numeral: ១៨ )
Komi-Permyak: даскыкьямыс ( daskykʹjamys )
Korean: 열여덟 (ko) ( yeoryeodeol ) , 십팔(十八) (ko) ( sip'pal )
Kurdish:
Central Kurdish: ھەژدە (ku) ( hejde )
Northern Kurdish: hejde (ku)
Kyrgyz: он сегиз (ky) ( on segiz )
Ladin: please add this translation if you can
Lakota: akéšagloǧaŋ
Lao: ສິບແປດ ( sip pǣt ) (numeral: ໑໘ )
Latin: octōdecim (la) , duodēvīgintī (la)
Latvian: astoņpadsmit (lv)
Ligurian: dixéutto
Lithuanian: aštuoniolika (lt)
Livonian: kōdõkstuoistõn
Lombard: please add this translation if you can
Louisiana Creole French: diz-wit
Low German: achtteihn German Low German: achtteihn
Luxembourgish: uechtzéng (lb)
Lü: ᦉᦲᧇᦶᦔᧆᧈ ( ṡiibṗaed¹ ) (numeral: ᧑᧘ )
Macedonian: осумна́есет ( osumnáeset )
Malagasy: valo ambinifolo
Malay: lapan belas (ms) , delapan belas (ms) , sepuluh lapan sepuluh delapan satu puluh lapan satu puluh delapan
Malayalam: പതിനെട്ട് (ml) ( patineṭṭŭ )
Maltese: tmintax
Mansi: нёлловхуйплов ( nëllovhujplov )
Maori: tekau mā waru (mi)
Mapudungun: maripura
Middle English: eiȝtetene
Mongolian: арван найм (mn) ( arvan najm )
Navajo: tseebíítsʼáadah
Norman: dix-huit dgiêx-huit
Northern Sami: gávccinuppelohkái
Norwegian: atten (no)
Occitan: dètz-e-uèch (oc)
Ojibwe: ashi-nishwaaswi
Old Church Slavonic: осмь на дєсѧтє ( osmĭ na desęte ) (numeral: и҃і )
Oriya: ଅଠର ( ôṭhôrô ) (numeral: ୧୮ ( 18 ) )
Pennsylvania German: achzeh achtzeh
Persian: هجده (fa) ( hejdah ) , هیجده (fa) ( hijdah )
Piedmontese: disdeut
Polish: osiemnaście (pl) , ( collective ) osiemnaścioro (pl)
Portuguese: dezoito (pt)
Punjabi: ਅਠਾਰਾਂ (pa) ( aṭhārā̃ )
Quechua: chunka pusaqniyuq
Romagnol: zdòt
Romani:
Kalo Finnish Romani: deȟ-o-oȟta
Romanian: optsprezece (ro)
Romansch: ( Grischun ) deschdotg
Russian: восемна́дцать (ru) ( vosemnádcatʹ )
Rusyn: вусямна́дцять ( vusjamnádcjatʹ )
S'gaw Karen: တဆံဃိး ( ta hsee xoḧ )
Samoan: sefulu valu
Sanskrit: अष्टादशन् (sa) ( aṣṭādaśan )
Santali: ᱜᱮᱞ ᱤᱨᱟᱹᱞ ( gel irăl )
Scottish Gaelic: ochd deug
Serbo-Croatian:
Cyrillic: осамнаест
Roman: osamnaest
Shan: သိပ်းပႅတ်ႇ ( síp pèt )
Sinhalese: දහඅට ( dahaaṭa )
Skolt Sami: käcmlo
Slovak: osemnásť (sk)
Slovene: osemnajst (sl)
Sorbian:
Lower Sorbian: wósymnasćo
Upper Sorbian: wósomnaće
Spanish: dieciocho (es)
Swedish: arton (sv) , aderton (sv) ( obsolete, Finnish Swedish )
Tagalog: labingwalo (tl)
Tahitian: hō'ē 'ahuru ma va'u
Tajik: ҳаждаҳ (tg) ( haždah )
Tatar: унсигез ( unsigez )
Telugu: పద్దెనిమిది (te) ( paddenimidi )
Thai: สิบแปด (th) ( sìp-bpɛ̀ɛt ) (numeral: ๑๘ )
Tibetan: བཅོ་བརྒྱད ( bco brgyad )
Tigre: ዐስር ወሰማን ( ʿäsr wäsäman )
Tigrinya: ዓሰርተ ሸሞንተ ( ʿasärtä šämontä )
Tongan: hongofulu mā valu
Turkish: on sekiz (tr)
Turkmen: on sekiz (tk)
Ukrainian: вісімна́дцять (uk) ( visimnádcjatʹ )
Urdu: اٹھارہ (ur) ( aṭhārah )
Uyghur: ئون سەككىز (ug) ( on sekkiz )
Uzbek: oʻn sakkiz (uz)
Vietnamese: mười tám
Vilamovian: aochcao
Volapük: degjöl balsejöl ( older term, obsolete )
Welsh: deunaw (cy) ( traditional ) , un deg wyth (cy) ( decimal )
West Frisian: achttjin (fy)
Wolof: fukk ak juróom ñett
Yakut: уон аҕыс ( uon ağıs )
Yiddish: אַכצן ( akhtsn )
Yup'ik: akimiaq pingayun
Zazaki: hestês desuhest
Zhuang: cib bet 
