Format - Uses str as a format specification, and returns the result of applying it to arg. If the format specification contains more than one substitution, then arg must be an Array containing the values to be substituted. See Kernel::sprintf for details of the format string. This is the default behavior of the String class.

• arg: an Array or other class except Hash.
• Returns: formatted String

 (e.g.) "%s, %s" % ["Masao", "Mutoh"]

Also you can use a Hash as the "named argument". This is recommanded way for Ruby-GetText because the translators can understand the meanings of the msgids easily.

• hash: {:key1 => value1, :key2 => value2, … }
• Returns: formatted String

 (e.g.) "%{firstname}, %{familyname}" % {:firstname => "Masao", :familyname => "Mutoh"}