I've checked Spanish, French, German, Portuguese and Polish, they all translate to "Secession War". On the other hand, in Russian and Greek they translate to "Civil War".
This is probably a niche question, but why the split? Is there a clear reason?
My first guess was to claim Confederate legitimacy, but one of the Spanish documents using the term shortly after the war, praises general Grant. So it's not obvious the relation. Maybe people simply considered it a secession war and didn't have any reason to avoid that term, in contrast to the US government?
If there is a variety of translations, it is likely because there was a variety of American names given to it. For quite a long time there was a disagreement over the name of the war in the US, just as there was a disagreement as to what it had been. For the official collection of Federal ( and some Confederate) documents relating to the war, issued by the War Department starting in 1880, it was called the War of the Rebellion, implying the Confederates were traitors taking up arms against the US government. Southerners who were "unreconstructed" ( had strong Confederate sympathies) would try to use the term "the War between the States", which carried the Lost Cause argument of the war being just a disagreement between the two regions. The term "Civil War" is therefore something of a compromise. Bertrand Russell might have said that the noun "war" is irregular, i.e. I am fighting for my rights, you are resorting to violence, they are murderous rebels.
There have been other examples. From 1967 to 1970 the Biafran region of Nigeria attempted to secede, and was defeated. That conflict is now called, in English, the Nigerian Civil War, the Biafran War, and the Nigerian-Biafran War. In each case, you can see an effort to cast the conflict into a different light just by changing the name. In French and German, though, it now seems to only be called the Biafran War.