You have posted this in a Thunderbird Support Forum which is manned by other Thunderbird users offering their time on an unpaid voluntary basis to help other Thunderbird users.

They generally do not help with language translations when it comes to creating new software or translations thereof. They may not have the same skills as yourself - maybe you could volunteer to help with the translations ?

Info at link: https://www.thunderbird.net/en-GB/participate/

A quick search found this:

https://www.1823.gov.hk/en/hong-kong-public-holidays-ical#:~:text=iCal%20is%20available%20in%20the%20following%20three,with%20most%20of%20the%20current%20calendar%20program.

I think this is the one you want: https://www.1823.gov.hk/common/ical/tc.ics

I am happy to contribute a version of the Hong Kong holiday calendar in the correct script. I would be grateful if someone can let me know to whom I should submit the corrected version. Thank you.