I totally agree. A loincloth (single word in English) is very very short, and often shows the backside. A kikoi is usually quite long and modest. It is a full wrap-around for the lower part of the body, usually for men. I would just use "kikoi" as was done for kanga and kitenge.
As far as I know, a kikoi is a garment worn by some men in the coastal regions of East Africa, and is similar to a traditional sarong. Some kikois are actually a sheet of cloth doubled over and sewn together joining two edges, so that you have to either pull it over your head, or possibly step into it. Then you wrap it around you, making an extra folds in front -- there's lots of spare cloth -- for additional modesty. It is nothing like a loin-cloth.