"区镇的地方长官" can be translated into English as "the local magistrate or official in charge of a district or town".
Here, "magistrate" often refers to a minor judicial officer or a local administrative official in some contexts, though its exact meaning can vary by country. A more general and inclusive term might be "local official in charge," which clearly conveys the idea of someone responsible for governing or administering a specific local area like a district or town.
If you want a more precise term that might vary by jurisdiction, you could also say "district/town administrator" or "district/town mayor" (depending on the specific role and title in the given context), as "mayor" typically refers to the head of a municipal government, and "administrator" can refer to someone responsible for managing the affairs of a district or town.
In summary, a suitable and commonly understood translation could be:
"The local official in charge of the district/town"
Or, more specifically based on the role: "District/Town Administrator" or "District/Town Mayor" (if applicable).