Add sketch of I18n error translation

lib/liquid/i18n.rb

@@ -0,0 +1,46 @@
+require 'yaml'
+require 'delegate'
+
+module Liquid
+  class I18n
+    class TranslationError < StandardError
+    end
+
+    def initialize(path)
+      @path = path
+    end
+
+    def translate(name, vars = {})
+      interpolate(deep_fetch_translation(name), vars)
+    end
+    alias_method :t, :translate
+
+    class << self
+      def translate(name, vars = {})
+        @@global.translate(name, vars)
+      end
+      alias_method :t, :translate
+
+      def global=(translator)
+        @@global = translator
+      end
+    end
+
+    private
+    def interpolate(name, vars)
+      name.gsub(/:(\w+)/) do
+        vars[$1.to_sym] or raise TranslationError, translate("errors.i18n.undefined_interpolation", :key => $1, :name => name)
+      end
+    end
+
+    def deep_fetch_translation(name)
+      name.split('.').reduce(locale) do |level, cur|
+        level[cur] or raise TranslationError, translate("errors.i18n.unknown_translation", :name => name)
+      end
+    end
+
+    def locale
+      @locale ||= YAML.load_file(@path)
+    end
+  end
+end