https://docs.joinmastodon.org/entities/Translation/ describes the following attributes in the response.

• content
• detected_source_language
• provider

According to implementation on mastodon.social at the time of writing (4.1.3+nightly-20230706) there is also:

• spoiler_text
• language (appears to be the language the text is translated into)
• poll (untested, but I assume this is a https://docs.joinmastodon.org/entities/Poll/ with options[.title] values translated)