@SindeeMThere is another problem with conversation in a foreign language, at least if its a contemporary story setting.
The author should be certain the sentence(s) are formulated as a native speaker of this language would speak, could even be spoken in a dialect of this language, but never be obviously bad translations of the English text. Too many of your readers may have enough knowledge of the language and put off by the attempt. Then it's better to write something like
So he asks in Italian to his partner, "What did they say?"
without actually using the Italian words.
It's not so problematic if the story is set in the far past or future. Spelling and grammar and word sense have changed in the last 800 years and will in the next 500 years to make it hard for most readers to distinguish between a bad translation and those time induced changes in the language.
Let me cite another author's thoughts about this:
Another comment worth discussion was that "the characters are not well educated, in some cases can't even read well, but use sophisticated words that they would be unlikely to know." I'm troubled by this, too. Mark Twain famously had uneducated characters using uneducated language, but that prose could be challenging to read. Another thing to consider is that modern, uneducated people often use many words specific to their community. Words that educated people don't know and find confusing.
Since I'm thinking of Ky's universe as a parallel world, splitting from ours in the Middle Ages and developing separately since then, we'd have to expect that much of their language wouldn't be understandable to us. After all, Shakespeare's actual writings are famously difficult for modern English speakers to read or hear—and he lived 500+ years after King Arthur. Thus, if you were to think too much about this, you'd have to conclude that what you're reading is my translation of their speech to our modern English and that such a translation might therefore include some words that modern uneducated people wouldn't use (and fail to include words present amongst Ky's contemporaries but unknown to us).
Someone quibbled over the use of the word "tire" to describe metal straps around wooden wheels. They actually were called tires back then, though it was originally spelled "tyre."
[Dahners, Laurence. Healer Magic]
HM.