Personally I would not try to "localise" this to the term used in Australia. I would simply use "Clerk" coupled with the appropriate description for the place concerned

Quel est le rôle du secrétaire général de la mairie ?
Il assiste le maire dans l'élaboration du budget. Il est le garant de son exécution. Il doit donc connaitre les règles budgétaires et comptables ainsi que le Code des marchés publics. Il s'occupe également du management des équipes et des ressources humaines.

Secrétaire de mairie : métier, études, diplômes, salaire ... - CIDJ

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Note added at 3 hrs (2023-08-25 18:14:58 GMT)
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ERI Economic Research Institute
https://www.erieri.com › salary › job › france
The average town clerk salary in France is 33 401 € or an equivalent hourly rate of 16 €. Salary estimates based on salary survey data collected directly ...

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Note added at 3 hrs (2023-08-25 18:16:15 GMT)
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town clerk - English-French Dictionary WordReference.com
WordReference.com
https://www.wordreference.com › enfr › town clerk
town clerk ; Principales traductions ; Anglais, Français ; town clerk, (town official), secrétaire de mairie nmf ...

I do a lot of certificate translations for Australian immigration and tend to localise this simply because it makes it immediately apparent to the department that the birth certificate has been issued in the 'normal' way. Or you could say Municipal Civil Registrar or Town Hall Civil Registrar perhaps... In my working languages I find that many different types of people fill this role, depending on the country - lots of secretaries or assistants to the Mayor in France, and lots of Notarios from Spanish speaking countries.

Here in Australia, the equivalent office is the Civil Registry and the person who makes the official record is the Civil Registrar, although I like Town Hall Clerk if you prefer not to localise it.

However, I noticed that your profile says you are based in Canada so I must give you a word of warning about translations for Australia - translation is a highly regulated profession over here and we have to be NAATI Certified in order to translate anything at all for official purposes.

If your client is using this translation to apply for an Australian visa from outside Australia then it's true that there is currently no restriction on who can do that translation, however if they are already in Australia then the Department of Immigration (and all other authorities) will only accept NAATI Certified translations.

This means that although a non-NAATI Certified translation may get them into the country, it will become unusable for anything else once they get here, including for things like opening a bank account/renting a place (if 2 forms of ID are required and they have no other suitable ID), enrolling in school/university, applying for a marriage licence, benefits, subsequent visas or citizenship etc. So it may not be a problem for you to do this translation if they are just intending to backpack for a while, but if they're moving themselves or their families here to live then it will likely become an issue. Many clients are completely unaware of this problem until they get to Australia and suddenly find that their documents start being rejected. They then have to pay to have everything re-translated by a NAATI Certified translator once they get here.

I hope this helps and I'm sorry if that's some unhappy news. Ultimately it is up to the client to ensure that they're buying a translation that will suit their purposes, but I always think it's good for business to give them all the info upfront as this may reflect back on you at some future point if they have to pay for retranslations. That said, this is exactly the sort of thing that translators outside Australia can't be expected to know, which is why I'm posting it here.

In North America, they say chief of staff instead of General Council manager

A Mayor's Chief of Staff is responsible for planning, organizing, managing, directing and overseeing the day-to-day operations of the Mayor's office and staff.