ch
gsw
ab-x-abc-a-a
ab-x-abc-x-abc
aed
apa
apa-CA
apa-Latn # ISO 639 can be 3-letters
ar-afb
az-Arab-x-AZE-derbend
de
de-015
de-a-value
de-AT
de-Bopo-DE
de-CH
de-CH-1901
de-CH-1996
de-DE-1901
de-Latg-1996
en
en-a-bbb-x-a-ccc
en-GB-boont-r-extended-sequence-x-private
en-GB-oed
en-Latn-GB-boont-r-extended-sequence-x-private
en-US
en-US-boont
en-US-x-twain
en-x-US
es-419
es-Latn-CO-x-private
fr
fr-FR
fr-Latn
fr-Latn-419
fr-Latn-CA
fr-Latn-FR
fr-y-myext-myext2
hy-Latn-IT-arevela
i-default # grandfathered
i-enochian # Grand fathered
i-klingon # grandfathered
I-kLINgon # tags are case-insensitive...
mn-Cyrl-MN
mN-cYrL-Mn
mn-Cyrl-MN
mN-cYrL-Mn
no
no-bok
sgn-aed
sl-IT-nedis
sl-Latn-IT-rozaj
sl-nedis
sr-Cyrl
sr-Cyrl-CS
sr-Cyrl-DE
sr-Latn
sr-Latn-CS
x-fr-CH
zh-cdo
zh-cmn
zh-cmn-Hans
zh-cmn-Hant
zh-cmn-Hant-HK
zh-gan
zh-yue
zh-yue-Hant-HK