> Using Latin phrases in law still feels too much like medieval clergy only reading the Bible in Latin and telling the laypeople to trust them.

It's a technical term with a fixed definition. It's not being interpreted, and it doesn't matter if it's English, Latin, or a drawing of a flower.

A lay person being able to guess at the meaning is a minor benefit in some situations, but people guess wrong all the time about how laws work. The end result is a pretty negligible difference.

And looking like normal words without actually being normal words can actually be a detriment to understanding.

> Using dead language for your jargon feels like it specifically keeps laypeople of the loop.

This is not really a fair assessment. Law and contracts aren’t all rewritten every few years — old and settled law must be read and understood in the style it was written in, as must precedents and contracts. At one time, the largest settled body of law was the Roman law and so a lot of Latin got dragged forward into the English legal system (and from there into the American, Hong Kong, Canadian, &c.).

The situation is like that in medicine, biology and many other sciences, where the long history of Latin as a language of scholarship is still felt in the choice of technical terms.

"This is not really a fair assessment"

Yes it is. Most people making an appeal wouldn't know what a prima facie case is. It is in fact how most self-done appeals fail in the first place. Most people don't know when they file for themselves to file pro se - a big failing for initial cases. Little technical crap like that which relies upon a dead language that only us geeks bothered taking in high school as their elective foreign language. WE get the advantage, the common person does not. Then to boot, we pretty much eliminated civics, so most people don't know how to file a lawsuit or defend themselves, let alone know the Latin terms to utilize in the first place!

And the NEW laws are still written in the OLD American English. No bueno.

Knowing what the words mean in Latin doesn't help you in any legal sense. You won't be able to present "at first sight evidence"(?!) in any useful manner without knowing the legal requirements and procedures. What you need to know is the law, and you're right, having that knowledge would help you when presenting a case....but that's a wholly different argument from knowing Latin.

You failed your translation - On The Face Of The Statement is the definition. Source: High school Latin.

I think the usage of Latin is very effective in this case; The meaning of the Latin words themselves is not important, the jargon is defined in legal texts and in the law. Meanwhile, the usage of Latin allows you to quickly identify which parts are legal doctrine - e.g. an "ex-parte decision" sounds like legal doctrine, "the judge made a decision without telling the other party" sounds like the judge had a grudge. I think in that sense, using a dead language is very appropriate; our jargon is a mixture of "kinda-like-but-not-quite" terms - memory, inheritance, relational, bus(actually a contraction of a Latin word), master/slave; and arcane words that might as well be Latin(multiplexer! polymorphism! bandwidth!). At least you can't really mistake the second group for anything but jargon.

While people might not have to interact with engineering jargon, they are often forced to interact with legal jargon at some of the worst times in their life; I think it's good signaling if they can easily identify whether someone's entering into a "legal interaction" with them rather than just a regular talk.

I think that's a really good point. Latin "terms of art" are automatically recognizable as such (and often even printed in italics to further set them apart). I see them as a notification that there is something specific meant by that term.

In contrast, English terms of art may be misleading based on their common interpretation - how often do people misunderstand "fair use" of copyrighted material?

Yes, but we're talking about Justice, not explanation. There could come a time where "the judge made a decision without telling the other party" is no longer a valid course of action in the justice system (i.e. not true justice.) Hiding that fact behind terminology no one understands is a problem.