Latin, the twenty-first language
Latin joins the list, with its own cast, its own sounds to learn, a voice and a course. It's the first language here that you can only learn: nobody speaks it as their own, so the app never speaks it to you. That makes twenty-one languages to learn, and still twenty to learn from.

Latin is now one of the languages the app teaches, which brings the list to twenty-one: Bulgarian, Chinese, Czech, Dutch, English, French, German, Greek, Hindi, Italian, Japanese, Korean, Latin, Polish, Portuguese, Romanian, Russian, Spanish, Swedish, Turkish and Ukrainian.
It arrives with everything the others have: a cast who speak it, a section for its sounds, a voice that reads words and examples aloud, and a course in the CEFR's levels, A1 to C2. It's also the first language here that only goes one way.
Learned, never spoken to you
Every other language here works in both directions. You can learn Japanese from Spanish, or Spanish from Japanese. Latin can't, because nobody speaks it as their own.
So the app never speaks Latin to you. It isn't in the list of languages you speak, and you can't learn another language from it. You learn Latin from English, or from any of the other nineteen.
Which Latin
The Church's, as the Vatican writes it today. That means its spelling: i for both the vowel and the consonant, u and v kept apart, and no long marks over the vowels. Where modern life needs a word, it's the one in the Vatican's own dictionary of new Latin words, not one made up for the occasion.
It's read the way the Church reads and sings it, which is the way an Italian would read it. If you learned Latin at school with every c hard, this will sound different: here caelum is "che-lum," and pacem is "pa-chem."
A voice borrowed from Italian
There's no Latin voice to use, so an Italian one reads it. First, the app rewrites the few spellings Latin has and Italian doesn't. Ae and oe become e. Ti before a vowel becomes zi, so gratia is read as grazia. Ph becomes f, y becomes i, and mihi keeps its hard sound as michi.
What you see doesn't change. The words stay as they're written; only what the voice is handed is respelled.
The sounds, not the letters
Latin is written with the letters you already know, so its letters section is about how they're said. There are twenty-five sounds in four groups: five pure vowels, the pairs written as two letters and said as one, the letters that change with the vowel after them, and the ones that are always read the same way. Each is learned by ear, in a word from the liturgy.
The people you meet
Nobody speaks Latin at home, so the cast are people who speak it by choice, in the places it's still spoken.
Iulia has come early to a café in Borgo Pio, a few streets from St. Peter's, where the Circulus Latinus Romanus meets on Thursday evenings to talk nothing but Latin. Don't call it a dead language in front of her.
Avia Livia taught Latin at the high school in Rieti for forty years and has never seen a reason to stop speaking it. She lives in a village in the Sabine hills, and she has put a bowl of ravioli in front of you before you've sat down.
Pater Basilius is a priest at Santa Sofia in Rome, a Ukrainian Greek-Catholic basilica. It follows the Byzantine rite, which is why it has domes, and it's in communion with Rome, which is why its priest studied theology in Latin. He greets you the way his church always has, Gloria Iesu Christo!, and waits for the answer: Gloria in saecula!
Grimar pours his ale, as he does everywhere.
Your teachers are Flavia, a university student who runs your drills, and Magistra Aurelia, who teaches your lessons at the chalkboard. The board dates the day the way the Vatican dates a document: Die XXI mensis Septembris.
Everyone is tu
Latin has one word for "you." The Romans said tu even to an emperor, so there's no polite form to learn, and no moment when someone decides you've earned the familiar one. Everyone says tu to you, and you say it to everyone.
The word you'll reach for is Italian
Every language here knows which neighbor leaks into it. For Latin it's Italian, which looks close enough that an Italian word slips in where a Latin one exists. The cast notice, and hand you the Latin one.
What comes next
The waitlist still asks which language you'd learn, and still offers "Something else" to anyone whose isn't there. That's how the next one gets picked.