The papal retirement news has proven that Latin is not totally useless: a Vatican reporter heard the news in Latin first and got the scoop. Similarly, back when the current Pope was elected, I was watching the announcement on TV and understood about a minute or two before everybody else who the new Pope was going to be and what his new Pope-name was.
For sources on Papal retirement/resignation/abdication, see this article by Fr. William Saunders and this Wikipedia article. It’s also useful, at times like these, to consult the Code of Canon Law of 1983:
- §1. The Roman Pontiff obtains full and supreme power in the Church by his acceptance of legitimate election together with episcopal consecration. Therefore, a person elected to the supreme pontificate who is marked with episcopal character obtains this power from the moment of acceptance. If the person elected lacks episcopal character, however, he is to be ordained a bishop immediately.
- §2. If it happens that the Roman Pontiff resigns his office, it is required for validity that the resignation is made freely and properly manifested but not that it is accepted by anyone.
Now, what’s this business about acceptance? There are other canons relevant to resignation of ecclesiastical office in general:
Anyone responsible for oneself (sui compos) can resign from an ecclesiastical office for a just cause.
A resignation made out of grave fear that is inflicted unjustly or out of malice, substantial error, or simony is invalid by the law itself.
- §1. To be valid, a resignation, whether it requires acceptance or not, must be made to the authority to whom it pertains to make provision of the office in question; this must be done either in writing, or orally in the presence of two witnesses.
- §2. The authority is not to accept a resignation which is not based on a just and proportionate cause.
- §3. A resignation which requires acceptance lacks all force if it is not accepted within three months; one which does not require acceptance takes effect when it has been communicated by the one resigning according to the norm of law.
- §4. A resignation can be revoked by the one resigning as long as it has not taken effect; once it has taken effect it cannot be revoked, but the one who resigned can obtain the office by some other title.
So, some resignations might require acceptance (189.1), presumably by the same authority that appointed the guy to the office (189.1?, 189.2), and sometimes the authority isn’t supposed to accept the resignation (189.2). Papal resignation, though, is one of those that doesn’t require acceptance, so the only requirements there are that it be free and properly manifested (332.2)
Now, about this “free[dom]” (332.2), perhaps this interacts with the requirement that you be sui compos (187)? So if you’re insane, maybe you can’t resign under 187, and maybe similarly this means you also can’t resign under 332.2. Though you’d think that’s when you’d most need someone to resign. Presumably there should be a procedure for this. Perhaps the general removal provisions of canons 192-194 would work here? Maybe someone who knows more canon law than I do could enlighten me. Also, it looks like even an insane Pope could get himself automatically removed from office by attempting marriage (194.3).
Somewhat relatedly, a British monarch can’t unilaterally abdicate: the succession statute says who’s king, and so an abdication requires another statute. When Edward VIII abdicated in 1936, the Commonwealth realms passed statutes to consent to the abdication, with the result that Edward VIII was king of Ireland for one day longer than he was king in Great Britain or anywhere else.
UPDATE: Sorry, accidentally said Code of 1978 instead of 1983. Thanks to commenter R Bellarmine.