Technically 2 separate issues:

1. The i18n string has a {3} instead of a {2}.
2. The meaning of the y-coordinate is rather unintuitive/unclear. By default //chunk will select the entire 0-255 space. Even in an extended-y situation (cubicchunks), giving the y-coordinate of "0" makes it seem like only a single chunk-section is selected, especially since the x and z coordinates may be given in chunk coords depending on command flags.