The algorithm for pluralizations in `:en` is as simple as:
```ruby
entry[count==1?0:1]
lookup_key=:zeroifcount==0&&entry.has_key?(:zero)
lookup_key||=count==1?:one::other
entry[lookup_key]
```
I.e. the translation denoted as `:one` is regarded as singular, the other is used as plural (including the count being zero).
The translation denoted as `:one` is regarded as singular, and the `:other` is used as plural. If the count is zero, and a `:zero` entry is present, then it will be used instead of `:other`.
If the lookup for the key does not return a Hash suitable for pluralization, an `I18n::InvalidPluralizationData` exception is raised.