Image source, Getty Images Image caption, Google's translation service handles one trillion words per month
"Il pleut des cordes," say the French when it's raining hard.
"It's raining ropes," is the direct translation. It's the kind of idiom which can trip up an AI translator.
"You can imagine the dilemma this throws AI into," says François Yvon, a research director specialised in automatic translation with the French National Centre for Scientific Research CNRS.
He says a well-trained system will know that ropes are not literally falling from the sky and use the English phrase "it's raining cats and dogs".
"But is it going to find the equivalent when it's translating into Indonesian?" asks Yvon.
A comment on the weather is pretty low-risk, but more and more translation is being done by machines, and on topics with higher stakes than the weather.
In April, Google said people are now translating , external one trillion words a month with Google Translate.
That doesn't count the others: DeepL, Microsoft, Claude, ChatCGT and Gemini, not to mention made-to-measure corporate translation systems.
Direct sales of machine translation , external (i.e. outside general AI subscriptions) were worth an estimated $1.4bn (£1bn) last year.
Image source, John Zimmerman Image caption, AI translation is the "right call" in many cases says John Zimmerman
"For plenty of use cases, raw AI translation is now the right call: multiplying your costs by 100 to catch the last few percent of errors isn't rational if you're translating internal documents or product listings," says John Zimmerman, founder of OKA (Open Knowledge Association), a Swiss non-profit that translates Wikipedia articles into other languages.
"For an encyclopedia it's different. Wikipedia runs on trust. A wrong fact can sit there for years and get cited by journalists and AI systems," he says.
With more than 10,000 published pieces, mostly into Spanish, Portuguese and English, OKA is, Zimmerman says, the single largest contributor of translated articles to the collaborative online encyclopedia.
Which is something it absolutely could not have become without AI.
"Translating 10,000 articles the traditional way would cost millions. In our process, the AI produces the draft, then a human translator checks every sentence," he explains.
But that human input is required less and less.
"The machine output is now good enough that skipping the human entirely has become a serious option, and a real temptation across the industry. Two or three years ago, with tools like DeepL, our translators still rewrote a good chunk of every draft.
"Today the prose often doesn't need fixing at all. So, the question is no longer whether AI translation is good, it clearly is, but whether it's good enough to remove the human," says Zimmerman.
Ariella Baltié is a translator and legal expert specialised in translating court documents from English into French.
She was contacted recently by someone who'd already translated his documents with AI, asking her to check them.
"There were two major errors right at the beginning," she said.
The AI had translated "Le demandeur" (the plaintiff) as "the requester". "Totally awkward for legal papers," says Baltié.
When the AI saw "Madame X, épouse Y" (Ms X, wife of Y'), it came up with "Ms X marries Y".
In other words, it mistook a noun for a verb, completely losing the meaning of the phrase.…