Description of problem:
The following languages are missing in languages.xml. references from language-subtag-registry from IANA:

Type: language
Subtag: ab
Description: Abkhazian
Added: 2005-10-16
Suppress-Script: Cyrl

Type: language
Subtag: av
Description: Avaric
Added: 2005-10-16

Type: language
Subtag: bin
Description: Bini
Description: Edo
Added: 2005-10-16

Type: language
Subtag: bm
Description: Bambara
Added: 2005-10-16

Type: language
Subtag: bua
Description: Buriat
Added: 2005-10-16
Scope: macrolanguage

Type: language
Subtag: ch
Description: Chamorro
Added: 2005-10-16
Suppress-Script: Latn

Type: language
Subtag: co
Description: Corsican
Added: 2005-10-16

Type: language
Subtag: cu
Description: Church Slavic
Description: Church Slavonic
Description: Old Bulgarian
Description: Old Church Slavonic
Description: Old Slavonic
Added: 2005-10-16

Type: language
Subtag: ee
Description: Ewe
Added: 2005-10-16

Type: language
Subtag: fat
Description: Fanti
Added: 2005-10-16
Macrolanguage: ak

Type: language
Subtag: gn
Description: Guarani
Added: 2005-10-16
Suppress-Script: Latn
Scope: macrolanguage

Type: language
Subtag: ho
Description: Hiri Motu
Added: 2005-10-16

Type: language
Subtag: hz
Description: Herero
Added: 2005-10-16

Type: language
Subtag: ie
Description: Interlingue
Description: Occidental
Added: 2005-10-16

Type: language
Subtag: ii
Description: Sichuan Yi
Description: Nuosu
Added: 2005-10-16

Type: language
Subtag: io
Description: Ido
Added: 2005-10-16

Type: language
Subtag: jv
Description: Javanese
Added: 2005-10-16

Type: language
Subtag: kaa
Description: Kara-Kalpak
Added: 2005-10-16

Type: language
Subtag: ki
Description: Kikuyu
Description: Gikuyu
Added: 2005-10-16

Type: language
Subtag: kj
Description: Kuanyama
Description: Kwanyama
Added: 2005-10-16

Type: language
Subtag: kr
Description: Kanuri
Added: 2005-10-16
Scope: macrolanguage

Type: language
Subtag: kum
Description: Kumyk
Added: 2005-10-16

Type: language
Subtag: kwm
Description: Kwambi
Added: 2009-07-29

Type: language
Subtag: lah
Description: Lahnda
Added: 2005-10-16
Scope: macrolanguage

Type: language
Subtag: lez
Description: Lezghian
Added: 2005-10-16

Type: language
Subtag: mh
Description: Marshallese
Added: 2005-10-16
Suppress-Script: Latn

Type: language
Subtag: mo
Description: Moldavian
Description: Moldovan
Added: 2005-10-16
Deprecated: 2008-11-22
Preferred-Value: ro
Suppress-Script: Latn

Type: language
Subtag: na
Description: Nauru
Added: 2005-10-16
Suppress-Script: Latn

Type: language
Subtag: ng
Description: Ndonga
Added: 2005-10-16

Type: language
Subtag: nqo
Description: N'Ko
Description: N’Ko
Added: 2006-06-05
Suppress-Script: Nkoo

Type: language
Subtag: nv
Description: Navajo
Description: Navaho
Added: 2005-10-16

Type: language
Subtag: ota
Description: Ottoman Turkish (1500-1928)
Added: 2005-10-16

Type: language
Subtag: rm
Description: Romansh
Suppress-Script: Latn
Added: 2005-10-16

Type: language
Subtag: rn
Description: Rundi
Added: 2005-10-16
Suppress-Script: Latn

Type: language
Subtag: sco
Description: Scots
Added: 2005-10-16

Type: language
Subtag: sel
Description: Selkup
Added: 2005-10-16

Type: language
Subtag: sg
Description: Sango
Added: 2005-10-16
Suppress-Script: Latn

Type: language
Subtag: sh
Description: Serbo-Croatian
Added: 2005-10-16
Scope: macrolanguage
Comments: sr, hr, bs are preferred for most modern uses

Type: language
Subtag: sma
Description: Southern Sami
Added: 2005-10-16

Type: language
Subtag: smn
Description: Inari Sami
Added: 2005-10-16

Type: language
Subtag: sms
Description: Skolt Sami
Added: 2005-10-16

Type: language
Subtag: sn
Description: Shona
Added: 2005-10-16

Type: language
Subtag: su
Description: Sundanese
Added: 2005-10-16

Type: language
Subtag: syr
Description: Syriac
Added: 2005-10-16
Scope: macrolanguage

Type: language
Subtag: tw
Description: Twi
Added: 2005-10-16
Macrolanguage: ak

Type: language
Subtag: ty
Description: Tahitian
Added: 2005-10-16

Type: language
Subtag: tyv
Description: Tuvinian
Added: 2005-10-16

Type: language
Subtag: vo
Description: Volapük
Added: 2005-10-16

Type: language
Subtag: vot
Description: Votic
Added: 2005-10-16

Type: language
Subtag: wen
Description: Sorbian languages
Added: 2005-10-16
Scope: collection

Type: language
Subtag: yap
Description: Yapese
Added: 2005-10-16

Type: language
Subtag: za
Description: Zhuang
Description: Chuang
Added: 2005-10-16
Scope: macrolanguage

Version-Release number of selected component (if applicable):
langtable-data-0.0.38-8.fc29.noarch

Additional info:
There might be more missing languages though those languages are used in fontconfig's orthography.