title and content (HTML, like a macro body). Keep the macro’s {{variables}} as written. options relabels the macro’s options by id; leave it out to keep the current translated labels. An option you don’t list is sent with its original label.
Your wording is used exactly like a generated translation: agents get it in the inbox for customers in that language. It is kept until the macro’s title, content or options change, or a custom variable it uses changes. Then the macro is translated again. Retranslate a macro also replaces it with a generated translation. Each change is recorded in the audit log.
The response is the macro’s translations, as returned by Get macro translations. It fails with 400 when the language is not one of the chosen ones, or is the language the macro is written in.