I think it depends on the office.
Some offices might be functionally English even in non-English-speaking regions: think Southeast Asia, some German offices, the pan-African offices, et cetera.
Others might be firmly lingoucentric (a word I just made up): think Paris, Istanbul, Sãa Paulo.
In the case of the former, expect the majority of your interviews to be in English. In south-east Asia, for example, 100% of my interviews where in English.
In the case of the latter, I would expect at least 50% of the interviews to be in the office's local language with at least one interview in English. I haven't got further specifics to back this up.
Of course, if you're interviewing in the Anglophones (Australia/US/London offices), expect to do everything in English unless you're applying for a unique, non-client facing role where fluency in another specific language has been specified.