`contentLanguages` disallows most non-lowercase language identifiers

[hoehrmann]

https://github.com/sdmx-twg/sdmx-json/blob/71fe5eaa9fcd29e3c15f2f0216a19b9b650b1dbd/data-message/docs/1-sdmx-json-field-guide.md uses language identifiers like en-GB, but the JSON Schema disallows such values, presumably by accident.

(In doubt, please handle this as a public review comment on SDMX 3.1 once the comment period begins.)

[dosse]

Thanks for the feedback. It seems that the regex expression used in the schema needs to be updated, e.g., with the regex expression here: https://www.regextester.com/103066