Should one denounce the offensive words or insults that may be uttered by foreigners in videos, whether inwardly or at the beginning of the video, or should one merely avoid hearing them?

The cure for waswasah (whispers of Shaytan/obsessive thoughts) is to disregard them, stop indulging them, and supplicate humbly to Allah, not by trying to cure them through seeking jurisprudential loopholes. The phrase "oh my god" has no religious objection. As for phrases that contain a religious prohibition, one must avoid listening to them, because witnessing an evil without necessity is forbidden, due to Allah's saying: "And He has already revealed to you in the Book that when you hear the verses of Allah being denied and ridiculed, do not sit with them until they enter into another conversation. Indeed, in that case, you would be like them." So, whoever witnesses an evil by choice is like its perpetrator, and it is forbidden to watch what is prohibited because it implies رضا (assent or approval). If one hears something forbidden unintentionally or out of necessity, one must denounce and detest it in their heart.