What is a plural? 1 file, 2 files, 3 files: file is singular, files plural. In this simple example we see the English plural form. Other languages have simpler or even more elaborate plural forms. Both KDE and Gettext have a method of managing plurals for PO files so that plurals can be used in languages that do not follow the English convention.
Why not just write a piece of code like this:
if ( n == 1 ) then print "1 file" else print "%d files", n
Well the simple answer is that not all languages follow the pluralisation format of English. Some use the singular form for both 0 and 1. Others have no singular/plural form. And yet others have complex systems that have at least 4 plural forms. For English speakers think of it as the different suffixes you see here: “1st, 2nd, 3rd, 4th ... 21st, 22nd, 23rd, 24th...”
So in order to cater for the various plural forms a system was developed.
If you have numbers in the singular and plural form then use the plural construct:
"%n file" "%n files"
However, if you do not have number in the construct then rather keep them as separate strings:
"Save the file" "Save the files"
On KDE with a 3 plural form language:
msgid "" "%n file\n" "%n files" msgstr "" "%n form 1\n" "%n form 2\n" "%n form 3"
Gettext with a two form language:
msgid "%n file" msgid_plural "%n files" msgstr "%n form 1" msgstr "%n form 2"
Also in Gettext style plurals the PO file header has an entry for the plural form which defines the number of plurals as well as the mathematical function to determine which one to use depending on the input number. Here is an example which would work for English:
"Plural-Forms: nplurals=2; plural=n == 1 ? 0 : 1;\n"
FIXME this looks set to change for KDE4 with the Gettext method most probably being adopted
i18n( "One item", "%n items", count);
Note that because KDE uses a n to split the different plural forms you cannot use n in the actual message. To work around this you can use KDE’s RichText features and the tag.
FIXME unsure how this is used