Any speakers of languages other than English wanna tell me if your language has an equivalent to these idoms?
The cat is out of the bag. Meaning “The secret is out.”
Cat got your tongue? Meaning “Are you unable to speak for some reason?”
When the cat’s away, the mice will play. Meaning, “When there is no authority figure around, those left unsupervised will engage in wrongdoing.”
Thanks.
Descubrirlo todo is the Spanish equivalent of letting the cat out of the back. An example of usage would be: Lo Descrubrió todo, which means he let the cat out of the back. Alternatively the infinitive: Revelar el secreto could be used.
I’ll see if I can find some more in my Spanish books somewhere. However not many idioms are directly translatable between languages, so instead of saying “Cat got your tongue?” You may want to say “No decir ni pio(sic.)” in Mexican Spanish, which just means to not say a word for some reason other than simply not wanting to.
Japanese only has the last one:
Oni no inuma ni sentaku, “while the devil’s away, do your washing”
The cat is out of the bag. - the German equivalent uses the same metaphor, but usually expressed with an explicit actor and the phrase die Katze aus dem Sack lassen (to let the cat out of the bag), e.g. X ließ endlich die Katze aus dem Sack (X finally let the cat out of the bag)
Cat got your tongue - no German equivalent metaphor that I know of. I’d use Hat es Dir die Sprache verschlagen? (has [implied agency] left you speechless?) in the situation.
When the cat’s away, the mice will play. - German equivalent Wenn die Katze aus dem Haus ist, tanzen die Mäuse (when the cat is out of the house, the mice dance)
For the first one, no direct equivalent in meaning comes to my mind in French at the time, there is “il a découvert le pot aux roses” (he discovered the pot with roses), meaning someone in particular discovered a secret.
For the last two, we say almost the exact same thing in French, except our mice are dancing instead of playing and the cat ate our tongues.
In finnish, the first one doesn’t really have an equivalent proverb, but ‘nostaa kissa pöydälle’, is kinda close, meaning to put the cat on the table, when it’s time to discuss something important, but which no one would want to discuss.
‘Kissako kielesi vei?’, is a direct translation of the english one, which was: ‘Cat got your tongue?’
The third one in finnish is 'Kun kissa on poissa, hiiret hyppii pöydällä," which in english goes: ‘When the cat is away, mice jump about on the table,’
Can’t think of anything approximating the first two just now, but the third one has a pretty close Dutch variant: Als de kat van huis is, dansen de muizen op tafel - When the cat’s [away] from house, the mice dance on the table.
ETA: the second one, of course, would be something along the lines of ‘ben je je tong verloren’ or ‘ben je je tong kwijt’ - did you lose your tongue?
I read recently about how the idiom “let the cat out of the bag” is related to the “pig in a poke” idiom…this wikipedia page explains the connection and lists a TON of foreign translations for the “pig in a poke” idiom, many of which use a “cat in a bag” wording. I assume the age of the “pig” idiom, which dates back to the Late Middle Ages, explains why it has made its way to so many different languages.
I believe I’ve heard “le chat est sorti du sac” before, but maybe it was influenced by the English expression.
Latin has several versions of “The mice will play…”
Bella gerunt mūrēs, ubi cattus nōn habet aedēs. - Mice carry on happily where the cat has no home.
*Insanīre facit mūrēs absentiā cattī. *- The mice make crazy in the absence of the cat.
Mūs salit in strātum, cum scit abesse cattum. - The mouse dances in the straw when he knows the cat is away.
Mūs debacchātur, ubi cattus nōn dominātur. - The mouse revels where the cat does not rule.
Quō nōn versantur cattī, mūrēs dominantur. - Where the cat does not dwell, the mice rule.
Because the Dark Lord is angered by clean sheets! 
The third one in French is Quand le chat n’est pas là, les souris dansent. Meaning, literally, “When the cat’s not there, the mice dance”.
As for the second one in French, the equivalent would be more like As-tu avalé ta langue?, “Did you swallow your tongue?”.
There is an expression, Donner sa langue au chat, “Give one’s tongue to the cat”, but you use it to admit you don’t know the answer to a (tricky, or in the context of a game) question you’ve been asked.
Vietnamese:
Cat out of the bag - no original idiom; they borrow this from us as far as I can tell.
Cat got your tongue - đi guốc trong bụng (the words are stuck in your stomach)
When the cat’s away… - chủ vắng nhà gà mọc đuôi tôm (when the boss is away, the workers will do anything but work)
None of these mention cats, although the last one involves shrimp and a chicken without its tail. Don’t ask me why. I’ve asked several native speakers and they can’t explain it to me either, except to say that the phrase came from Chinese originally.
In Cantonese:
The cat is out of the bag. 穿咗煲 (tsün dzo boh). It literally means “the pot has been pierced”.
Cat got your tongue? Can’t think of any idiom off hand.
When the cat’s away, the mice will play. 冇皇管 (moh wong gwun) It means “not governed by any king”.
“vendre la mèche” = let the cat out of the bag in French.
Can’t come up with anything in Swedish for the first two, but the third is “När katten är borta dansar råttorna på bordet”, “When the cat is away the rats dance on the table”.
Hebrew:
The cat is out of the bag: The awl is out of the bag. The idea is that the awl is a very sharp implement, and will eventually drill a hole in the bag whether you want to expose it or not.
However, buying something sight unseen is called “buying a cat in a bag,” which is apparently related to the eventual exposure of the cat…
Cat got your tongue? Swallowed your tongue?
When the cat’s away, the mice will play Translated into Hebrew as-is.
And the first one would be: De aap komt uit de mouw, which means the monkey is comming out of the sleeve…yeah…
In Spain, we have the following idioms, which I think are similar in meaning to the English ones mentioned in the OP.
For “The cat is out of the bag”, we can have "estirar de la manta" (to pull the blanket off). This means, however, to deliberately reveal some secret that someone else doesn’t want revealed. Acting like a whistleblower, in other words.
“El contable amenazó al presidente del banco diciendo que, si le detenían, estiraría de la manta” (“The accountant threatened the president of the bank by saying that, if the police were to arrest him, he would reveal everything he knows”)
For “Cat got your tongue?” we have "¿Te ha comido la lengua el gato?" (“Has the cat eaten your tongue?”). It means the same as in English (i.e., being tongue-tied).
“Hijo, háblame, díme qué ha pasado… ¿te ha comido la lengua el gato, acaso?” (“Son, talk to me, tell me what happened… The cat got your tongue, or what?”).
For “When the cat is out, the mice will play” we have "Cuando el gato no está, los ratones hacen fiesta" (“When the cat is not there, the mice will have a party”). Same meaning as in English.
“El jefe se fue a mediodía, y ya sabes… Cuando el gato no está, los ratones hacen fiesta” (“The boss left at noon, and you know… when the cat is out, the mice will play”).