I have always taught my students that "toto" was the French equivalent of "foo" for naming a file or a variable when you don't want to be bothered coming up with a name. Although true in practice, in reality the two words have very different origins.
"foo" is supposedly a misspelling of "f.u.", an acronym for "fucked up" as comes up in the military slang term "s.n.a.f.u." or "f.u.b.a.r.", "situation normal, all fucked up" and "fucked up beyond all repair".
"toto" has a less controversial etymology. It comes from the name of a young boy, the main character in a 19th century play. Nowadays Toto usually appears in childish jokes. It is roughly analogous to "Johnny". When I was 6 or 7 years old my friends and I at school exchanged many jokes about Toto, usually involving pee and poop.
On the other hand, another possible origin of "foo", also from WW2, is that apparently, wherever British troops went, the graffito “FOO was here” frequently showed up. I tend to believe that simply because in that case "foo" and "toto" would have more similar origins.
What is used in other languages? The automatic translation tools don't work for foo!