https://www.hjp.at/doc/rfc/rfc4645.html
hjp: doc: RFC 4645: Initial Language Subtag Registry
hjpdocrfcinitiallanguage
https://code.icod.de/dalu/language-subtag-registry/?display=rendered
dalu/language-subtag-registry - code.icod.de
language-subtag-registry
dalulanguagesubtagregistrycode
https://rocketvalidator.com/html-validation/bad-value-x-for-attribute-lang-on-element-y-bad-script-subtag
HTML check: Bad value X for attribute “lang” on element “y”: Bad script subtag. · Rocket Validator
Guide describing the HTML issue detected by the W3C Validator: Bad value X for attribute “lang” on element “y”: Bad script subtag.
htmlcheckbadvalueattribute
https://baselinealignment.section508.gov/testcases/TC15.B-3-fail-1.html
Language of Parts - Invalid language subtag
languagepartsinvalidsubtag