In my writing there are eight groups of people, each with their own language that they speak. Do I put large amounts of writing into their language or english? Do I write it first in theirs, then in english, or do I just write it in english and forget about the original language?
POV, POV, POV
The POV is important when doing that. Who says what? Who understands? What is the outcome?
If the story is from one perspective, then the narrator would say something like
The Japanese talked among themselves before they replied. "Yes, we can do." Seeing that, the French began to chatter, waving their hands wildly in a heated discussion. The Indians nodded to each other speaking in low tones.
If the exact dialogue is important, then you change the PoV.
"We should do it, " said Tanaka
"Can we complete it in time?"
"It will be difficult, but yes"
Tanaka stepped forward and announced "Yes, we can do," in his broken English. That triggered reactions across the room.
Hearing the Japanese' response, Pierre was livid, he was certain they would not agree. [...]
If everything happens at the same time, then you can make short time jumps back in time
I would avoid putting in too many languages. I know some people get away with it, but what are the odds of someone, who bought an English novel, speaking Japanese, French, Italian, and Pashtu? I'd have to say, pretty small.
Then comes your ability to write in these languages on the level of the speaker. If one person is well-versed, they'll call you out on something not adding up and it can break immersion (kind of a big thing for most readers).
So, my advice, is avoid putting in the 'other language' if you can (and I can't think of one reason why you can't). JP Chapleau explained it well enough how to get it all across without actually writing in the 'target language'.
One tactic some might find interesting, is writing in the the target language, and 'sub titling' it to explain what's going on. But it's hard to do unless your point of view character can reasonably (<-- important word right there) understand all eight languages. Be honest, how many people speak 8 languages? IRL? Not many. In fiction? Groans way too many. In Star Wars KOTOR, the main character spoke... what was it, 1500? I think "an impressive amount of alien languages" shouldn't be anything but Mary-Sue red flag.
You might look at "War and Peace" to see the effect of large parts of text being written in a foreign language: it is a book in Russian, with a significant part of the dialogues between nobles being in French. When Tolstoy was writing this, he could expect his readers to be bilingual. Nowadays, Russian publications all have the French sections translated into Russian in the footnotes, while translations to other languages get to choose between this, and just translating the whole thing straight, and marking the relevant parts as "having been in French". So, as a reader, unless you're bilingual, you'd be reading the whole text in one language, only some of it would be more clunky. Which seems to suggest "forget the original language". JP Chapleau gives a good explanation of how to do this.
There are exceptions, of course. Tolkien incorporates into his writing phrases, and even whole poems, in the elven languages, sometimes translated, other times not. The reader, obviously, is not supposed to understand what is being said in those cases. Neither does the POV character. The purpose of those (very brief) inserts is not merely to say "elves speak a foreign language". It is to convey a pleasant (or unpleasant when it's Dark Speech) sound of a language, the words of which are not understood. You might, for example, have a character saying something in a foreign language that sounds like something else in English, causing a misunderstanding. In that case, you'd want to incorporate the foreign language, as it is the sound that's important, not the content of what's being said.