BCP 47 language tags

BCP47-locales.md

Language Tag	Language	Region	Description
ar-SA	Arabic	Saudi Arabia	Arabic (Saudi Arabia)
bn-BD	Bangla	Bangladesh	Bangla (Bangladesh)
bn-IN	Bangla	India	Bangla (India)
cs-CZ	Czech	Czech Republic	Czech (Czech Republic)
da-DK	Danish	Denmark	Danish (Denmark)
de-AT	German	Austria	Austrian German
de-CH	German	Switzerland	"Swiss" German
de-DE	German	Germany	Standard German (as spoken in Germany)
el-GR	Greek	Greece	Modern Greek
en-AU	English	Australia	Australian English
en-CA	English	Canada	Canadian English
en-GB	English	United Kingdom	British English
en-IE	English	Ireland	Irish English
en-IN	English	India	Indian English
en-NZ	English	New Zealand	New Zealand English
en-US	English	United States	US English
en-ZA	English	South Africa	English (South Africa)
es-AR	Spanish	Argentina	Argentine Spanish
es-CL	Spanish	Chile	Chilean Spanish
es-CO	Spanish	Colombia	Colombian Spanish
es-ES	Spanish	Spain	Castilian Spanish (as spoken in Central-Northern Spain)
es-MX	Spanish	Mexico	Mexican Spanish
es-US	Spanish	United States	American Spanish
fi-FI	Finnish	Finland	Finnish (Finland)
fr-BE	French	Belgium	Belgian French
fr-CA	French	Canada	Canadian French
fr-CH	French	Switzerland	"Swiss" French
fr-FR	French	France	Standard French (especially in France)
he-IL	Hebrew	Israel	Hebrew (Israel)
hi-IN	Hindi	India	Hindi (India)
hu-HU	Hungarian	Hungary	Hungarian (Hungary)
id-ID	Indonesian	Indonesia	Indonesian (Indonesia)
it-CH	Italian	Switzerland	"Swiss" Italian
it-IT	Italian	Italy	Standard Italian (as spoken in Italy)
ja-JP	Japanese	Japan	Japanese (Japan)
ko-KR	Korean	Republic of Korea	Korean (Republic of Korea)
nl-BE	Dutch	Belgium	Belgian Dutch
nl-NL	Dutch	The Netherlands	Standard Dutch (as spoken in The Netherlands)
no-NO	Norwegian	Norway	Norwegian (Norway)
pl-PL	Polish	Poland	Polish (Poland)
pt-BR	Portuguese	Brazil	Brazilian Portuguese
pt-PT	Portuguese	Portugal	European Portuguese (as written and spoken in Portugal)
ro-RO	Romanian	Romania	Romanian (Romania)
ru-RU	Russian	Russian Federation	Russian (Russian Federation)
sk-SK	Slovak	Slovakia	Slovak (Slovakia)
sv-SE	Swedish	Sweden	Swedish (Sweden)
ta-IN	Tamil	India	Indian Tamil
ta-LK	Tamil	Sri Lanka	Sri Lankan Tamil
th-TH	Thai	Thailand	Thai (Thailand)
tr-TR	Turkish	Turkey	Turkish (Turkey)
zh-CN	Chinese	China	Mainland China, simplified characters
zh-HK	Chinese	Hong Kong	Hong Kong, traditional characters
zh-TW	Chinese	Taiwan	Taiwan, traditional characters

es-CO it is Colombia, not Columbia

Thanks

This is odd: the EPUB3 specification says to use BCP 47 language codes. Two-letter indexes are given as examples (here, here, here and here). However, here you give four-letter designations, calling them BCP 47 language tags.

What is the reason for the discrepancy?