What is the ruling on working for a foreign company where one knows that thefts and other illicit activities occur, given that reporting this would lead to great discord?

You must strive to rectify the thefts to the best of your ability, either by direct advice or by alerting those who have influence over them, while clarifying the gravity of their actions. However, if your words would lead to a greater harm, then you must refrain from speaking, because warding off harm takes precedence over gaining benefits.

Al-’Izz ibn Abd al-Salam said: "If benefits and harms converge, and it is possible to achieve the benefits and ward off the harms, we do so, in compliance with the verse: ﴿So fear Allah as much as you are able.﴾ And if it is impossible to ward off the harms and achieve the benefits, then if the harm is greater than the benefit, we ward off the harm, in accordance with what Allah says about intoxicants and gambling: ﴿Say, 'In them is great sin and [yet some] benefits for people. But their sin is greater than their benefit.'﴾ And if the benefit is greater, we achieve the benefit while enduring the harm."

Therefore, if pointing out the thefts leads to a greater harm, you should turn away from it and strive to minimize the evil as much as you can.