Air Crash Investigation

I was introduced to this series on the Smithsonian channel by a friend. Really like it because I enjoy flying & have learned a lot. Never knew English was the language "of the air" with all the manuals, checklists & instruments in English. I have wondered, though, how the multi-national crash investigations are handled, especially when the actual investigator is interviewed with sub-titles because they cannot speak English or are not fluent. I remember the episode of a French Caribbean airline departing Panama and crashing in Venezuela.. I could only imagine how those investigations were handled... English?