WikipediaThe Free Encyclopedia – is "the free wiki encyclopedia that anyone can edit". Brainchild of Jimmy Wales (and others); and the original project of the subsequent Wikimedia Foundation (WMF), Wikipedia strives claims to have an officially 'neutral point of view' (NPOV); but is often accused by people on each side of the political or other spectrums of being biased towards the other side. Wikipedia is the biggest fish in the global wiki pond, and receives far more traffic, and editing activity, than any other wiki. However, despite Wikipedias' claim to being an 'encyclopedia'; many academic institutes and other professional organisations recommend that Wikipedia is not used as a primary source of information, due to the fact that many articles are frequently incorrect, and many articles have a seemingly extremely low threshold of 'reliable source' references and citations! Indeed, many Wikipedia articles fail their own verifiability criteria, and can remain for many years without any citations, dispite warning banners highlighting the lack of said citations (and threatening to delete said unreferenced articles), and this even includes biographical articles for living people . . . and the English Wikipedia allows articles to be 'promoted' to a good article (GA) status despite failing their own criteria on having adequate reliable source citations, editorial conjecture, and even original research!

Historically, when Wikipedia was founded, it released all textual wiki content under the GNU Free Documentation License (GFDL). However, during 2009, existing Wikipedia wikis migrated to a new license – the Creative Commons Attribution-Share Alike 3.0 unported license (CC-BY-SA 3.0); and all content published until that migration date could be retro-released under either or both licenses. All content published after the migration date is released under only the CC-BY-SA 3.0 license, as are any newly created Wikipedia language versions. [1]

See also
All Wikipedias in these languages: (edit)

As of March 2013, Wikimedia Meta-Wiki indicates that there are 285 Wikipedias of different languages, and also groups them by size.

1 000 000+:ref Deutsch (de), English (en), Français (fr), Italiano (it), Nederlands (nl)
100 000+:ref العربية (ar), Български (bg), Català (ca), Sinugboanon (ceb), Česky (cs), Dansk (da), Esperanto (eo), Español (es), Eesti (et), Euskara (eu), فارسی (fa), Suomen kieli (fi), Galego (gl), עברית ויקיפדיה|עברית (he), हिन्दी (hi), Hrvatska (hr), Magyar (hu), Bahasa Indonesia (id), 日本語 (ja), Қазақша (kk), 한국어 (ko), Lietuvių (lt), Bahasa Melayu (ms), Norsk (Bokmål) (no), Polski (pl), Português (pt), Română (ro), Русский (ru), Slovenčina (sk), Slovenščina (sl), Српска (sr), Svenska (sv), Türkçe (tr), Українська (uk), Tiếng Việt (vi), Volapük (vo), Winaray (war), 中文 (zh)
10 000+:ref Afrikaans (af), Alemannisch (als), Ahmaric (am), Aragonés (an), Egyptian Arabic (arz), Asturianu (ast), Azərbaycan (az), Башҡорт (ba), Žemaitėška (bat-smg), Беларуская (be), Беларуская (тарашкевіца) (be-x-old), বাংলা (bn), ইমার ঠার/বিষ্ণুপ্রিয়া মণিপুরী (bpy), Brezhoneg (br), Bosanska (bs), Basa Ugi (bug), Soranî / کوردی (ckb), Чăваш (cv), Cymraeg (cy), Ελληνικά (el), Frysk (fy), Gaeilge (ga), Gàidhlig (gd), ગુજરાતી (gu), Fiji Hindi (hif), Krèyol Ayisyen (ht), Հայերեն (hy), Interlingua (ia), Ido (io), Íslenska (is), Basa Jawa (jv), ქართული (ka), ಕನ್ನಡ (kn), Kurdî / كوردی (ku), Кыргызча (ky), Vicipædia (la), Lëtzebuergesch (lb), Lombart (lmo), Latviešu (lv), Basa Banyumasan (map-bms), Malagasy (mg), Македонски (mk), മലയാളം (ml), मराठी (mr), Burmese (my), مَزِروني (mzn), Napulitano (nap), Plattdüütsch (nds), नेपाली (ne), नेपाल भाषा (new), Nynorsk (nn), Occitan (oc), Piemontèis (pms), Punjabi (pnb), Runa Simi (qu), Armãneashce (roa-rup), Sicilianu (scn), Scots (sco), Srpskohrvatski / Српскохрватски (sh), Simple English (simple), Shqip (sq), Basa Sunda (su), Kiswahili (sw), தமிழ் (ta), Telugu (te), Тоҷикӣ (tg), ไทย (th), Tagalog (tl), Tatarça (tt), اردو (ur), O‘zbek (uz), Walon (wa), Yorùbá (yo), Bân-lâm-gú (zh-min-nan), 粵語 (zh-yue)
1 000+:ref Bahsa Acèh (ace), Eald Englisc (ang), ܐܪܡܝܐ (arc), অসমীয়া (as), Авар (av), Aymar (ay), Boarischn (bar), Central Bicolano (bcl), भोजपुरी (bh), Banjar (bjn), བོད་སྐད (bo), Буряад (bxr), Chavacano de Zamboanga (cbk-zam), Нохчийн (ce), Corsu (co), Qırımtatarca (crh), Kashubian (csb), Zazaki (diq), Dolnoserbski (dsb), ދިވެހިބަސް (dv), Emiliàn e rumagnòl (eml), Estremeñu (ext), Võro (fiu-vro), Føroyskt (fo), Arpitan (frp), North Frisian (frr), Furlan (fur), Gagauz (gag), 贛語 (gan), گیلکی (glk), Avañe'ẽ (gn), Gaelg (gv), Hak-kâ-fa / 客家話 (hak), Hawai`i (haw), Hornjoserbsce (hsb), Interlingue (ie), Ilokano (ilo), Lojban (jbo), Taqbaylit (kab), Kalaallisut (kl), Khmer (km), Komi-Permyak (koi), Къарачай-Малкъар (Qarachay-Malqar) (krc), Ripuarian (ksh), Коми (kv), Kernewek (kw), Dzhudezmo (lad), Lak (lbe), Lezgian (lez), Limburgs (li), Líguru (lij), Lingála (ln), Мокшень (Mokshanj Kälj) (mdf), Олык Марий (Olyk Marij) (mhr), Māori (mi), Монгол (mn), Hill Mari (mrj), Malti (mt), Эрзянь (Erzjanj Kelj) (myv), Nahuatl (nah), Nedersaksisch (nds-nl), Novial (nov), Normaund (nrm), Diné bizaad (nv), ଓଡ଼ିଆ (or), Ирон æвзаг (os), ਪੰਜਾਬੀ (pa), Pangasinan (pag), Kapampangan (pam), Papiamentu (pap), Picard (pcd), Deitsch (pdc), Palatinate German (pfl), पाऴि (pi), پښتو (ps), Rumantsch (rm), Tarandíne (roa-tara), Rusyn (rue), Ikinyarwanda (rw), संस्कृतम् (sa), Саха тыла (sah), Sardu (sc), Sámegiella (se), Sinhalese (si), Shona (sn), Soomaaliga (so), Sranantongo (srn), Seeltersk (stq), Ślůnski (szl), تركمن (tk), Faka Tonga (to), Tok Pisin (tpi), Удмурт (udm), Oyghurque (ug), Vèneto (vec), Vepsian (vep), West-Vlams (vls), Wolof (wo), 吴语 (wuu), Хальмг (xal), Mingrelian (xmf), ייִדיש| (yi), Zeêuws (zea), 古文 / 文言文 (zh-classical)
100+:ref Аҧсуа (ab), Akana (ak), Bislama (bi), Bamanankan (bm), Mìng-dĕ̤ng-ngṳ̄ (cdo), Chamoru (ch), Cherokee (chr), Cheyenne (chy), Nehiyaw (cr), Словѣньскъ (cu), ཇོང་ཁ (dz), Eʋegbe (ee), Fula (ff), Fijian (fj), Gothic (got), هَوُسَ (ha), Igbo (ig), Iñupiak (ik), ᐃᓄᒃᑎᑐᑦ (iu), Qaraqalpaqsha (kaa), Kabardian Circassian (kbd), KiKongo (kg), Gĩkũyũ (ki), कश्मीरी / كشميري (ks), Luganda (lg), ລາວ (lo), Latgalian (ltg), Молдовеняскэ (mo), Mirandesa (mwl), Dorerin Naoero (na), Northern Sotho (nso), Chichewa (ny), Oromoo (om), Norfuk (pih), Ποντιακά (pnt), romani - रोमानी (rmy), Kirundi (rn), سنڌي، سندھی ، सिन्ध (sd), Sängö (sg), Gagana Samoa (sm), SiSwati (ss), Sesotho (st), Tetun (tet), Tigrinya (ti), Setswana (tn), Xitsonga (ts), Tumbuka (tum), Twi (tw), Reo Mā`ohi (ty), Tshivenda (ve), isiXhosa (xh), Cuengh (za), isiZulu (zu)
10+:ref Choctaw (cho), Sichuan Yi (ii), Marshallese (mh), Ndonga (ng)
1+:ref Afar (aa), Hiri Motu (ho), Kuanyama (kj), Kanuri (kr), Muscogee (mus)
0 articles in language (other than main page):ref Herero (hz)
Depreciated:ref tlhIngan Hol (Klingon) (tlh), Toki Pona (tokipona)

Other: Wikipedia 10, Wikipedia Test Wiki, test2.Wikipedia, Nostalgia Wikipedia, In Memoriam

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Try to keep this on track; have a look at list of Wikipedias on meta-wiki