In the API modules for Wikibase there is a entry for valid languages, and it is defined like this
languages - By default the internationalized values are returned in all available languages. This parameter allows filtering these down to one or more languages by providing one or more language codes.
Values (separate with '|'): aa, ab, ace, af, ak, aln, als, am, an, ang, anp, ar, arc, arn, ary, arz, as, ast, av, avk, ay, az,
azb, ba, bar, bat-smg, bcc, bcl, be, be-tarask, be-x-old, bg, bh, bho, bi, bjn, bm, bn, bo, bpy,
bqi, br, brh, bs, bug, bxr, ca, cbk-zam, cdo, ce, ceb, ch, cho, chr, chy, ckb, co, cps, cr, crh,
crh-latn, crh-cyrl, cs, csb, cu, cv, cy, da, de, de-at, de-ch, de-formal, diq, dsb, dtp, dv, dz, ee,
egl, el, eml, en, en-ca, en-gb, eo, es, et, eu, ext, fa, ff, fi, fit, fiu-vro, fj, fo, fr, frc, frp,
frr, fur, fy, ga, gag, gan, gan-hans, gan-hant, gd, gl, glk, gn, got, grc, gsw, gu, gv, ha, hak,
haw, he, hi, hif, hif-latn, hil, ho, hr, hsb, ht, hu, hy, hz, ia, id, ie, ig, ii, ik, ike-cans,
ike-latn, ilo, inh, io, is, it, iu, ja, jam, jbo, jut, jv, ka, kaa, kab, kbd, kbd-cyrl, kg, khw, ki,
kiu, kj, kk, kk-arab, kk-cyrl, kk-latn, kk-cn, kk-kz, kk-tr, kl, km, kn, ko, ko-kp, koi, kr, krc,
kri, krj, ks, ks-arab, ks-deva, ksh, ku, ku-latn, ku-arab, kv, kw, ky, la, lad, lb, lbe, lez, lfn,
lg, li, lij, liv, lmo, ln, lo, loz, lt, ltg, lus, lv, lzh, lzz, mai, map-bms, mdf, mg, mh, mhr, mi,
min, mk, ml, mn, mo, mr, mrj, ms, mt, mus, mwl, my, myv, mzn, na, nah, nan, nap, nb, nds, nds-nl,
ne, new, ng, niu, nl, nl-informal, nn, no, nov, nrm, nso, nv, ny, oc, om, or, os, pa, pag, pam, pap,
pcd, pdc, pdt, pfl, pi, pih, pl, pms, pnb, pnt, prg, ps, pt, pt-br, qu, qug, rgn, rif, rm, rmy, rn,
ro, roa-rup, roa-tara, ru, rue, rup, ruq, ruq-cyrl, ruq-latn, rw, sa, sah, sat, sc, scn, sco, sd,
sdc, se, sei, sg, sgs, sh, shi, shi-tfng, shi-latn, si, simple, sk, sl, sli, sm, sma, sn, so, sq,
sr, sr-ec, sr-el, srn, ss, st, stq, su, sv, sw, szl, ta, tcy, te, tet, tg, tg-cyrl, tg-latn, th, ti,
tk, tl, tly, tn, to, tokipona, tpi, tr, tru, ts, tt, tt-cyrl, tt-latn, tum, tw, ty, tyv, udm, ug,
ug-arab, ug-latn, uk, ur, uz, ve, vec, vep, vi, vls, vmf, vo, vot, vro, wa, war, wo, wuu, xal, xh,
xmf, yi, yo, yue, za, zea, zh, zh-classical, zh-cn, zh-hans, zh-hant, zh-hk, zh-min-nan, zh-mo,
zh-my, zh-sg, zh-tw, zh-yue, zu
In this list there are entries that should not be used for language specific entries, like the Norwegian (no) entry. This is a metalanguage for Bokmål (nb) and Nynorsk (nn). I guess there are several others that is also wrong. Some of them could be redirected, but some should not be used at all. If the entry is used as a site-prefix, or in the site id, we should probably set up a redirect even if it is not strictly correct.
Version: unspecified
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=42153