I've seen the term "foreign rights agent" bandied about recently, and I actually don't know what this means. Can you explain the difference between a regular agent and a foreign rights agent? And do I need to query both?
Firstly, no. You do not have query a foreign rights agent.
Foreign rights agents work with books that have already been published (or are about to be published) and arrange for those books to be made available in territories outside the original publisher's home. For example, a book that was published in New Zealand may not immediately be available in the US because the rights to the US territory have not been sold. A foreign rights agent would broker that deal.
Foreign rights agents may also deal with translators to ensure a book written in English can be accessed by readers in France or Germany or Brazil in those readers' native language. And that books written in languages other than English are translated and made available to English-speaking readers.
Foreign rights agents have specialised skills and knowledge of the markets in which they represent titles. And not all foreign rights agents will have this insight into all international territories. Agents tend to specialise in particular markets and rely on co-agents who have inside knowledge of other markets for sales outside their key territories.
Markets can be fickle and change often, so a foreign rights agent will be in frequent contact with international publishers to ensure they find the right home for the books they are representing. Foreign rights agents are also likely to attend international book fairs to check out what kinds of books are being published in different territories.
So, in a nutshell, a foreign rights agent is the middleman between your domestic publisher, and a publisher in another territory. Some authors prefer to retain their foreign rights so they can engage their own foreign rights agent and work with them directly, while others will assign these rights to their publisher who will then commission a foreign rights agent to represent their collection of titles.
I hope that helps!