How do I internationalize/localize my rails plugin?

I wrote a validates_word_count plugin. I would like to store the error messages in a YAML file so they can be easily translated.

Full source:
https://github.com/paulschreiber/validates_word_count/

My plugin’s file layout looks like this:
validates_word_count/
init.rb
lib/
validates_word_count.rb
locale/
en.yml

My YAML file looks like this:
en:
validates_word_count:
errors:
messages:
too_few_words: “has too few words (minimum is %d words)”
too_many_words: "has too many words (maximum is %d words)”

However, if I call I18n.translate(‘validates_word_count.errors.messages.too_few_words’), I get this error:
translation missing: en, validates_word_count, errors, messages, too_few_words

How can I set up my plugin / locale so I18n.translate() works?

Paul