PERF: only load locale files we are using

We used to load up all translations in all languages

app/models/locale_site_setting.rb

@@ -20,5 +20,4 @@ class LocaleSiteSetting < EnumSiteSetting
     end
   end
 
-  private_class_method :supported_locales
 end

lib/freedom_patches/translate_accelerator.rb

@@ -1,4 +1,35 @@
+# This patch performs 2 functions
+#
+# 1. It caches all translations which drastically improves
+#    translation performance in an LRU cache
+#
+# 2. It patches I18n so it only loads the translations it needs
+#    on demand
+#
+# This patch depends on the convention that locale yml files must be named [locale_name].yml
+
 module I18n
+  module Backend
+
+    class Simple
+      def available_locales
+        # in case you are wondering this is:
+        # Dir.glob( File.join(Rails.root, 'config', 'locales', 'client.*.yml') )
+        #    .map {|x| x.split('.')[-2]}.sort
+        LocaleSiteSetting.supported_locales.map(&:to_sym)
+      end
+    end
+
+    module Base
+      # force explicit loading
+      def load_translations(*filenames)
+        unless filenames.empty?
+          filenames.flatten.each { |filename| load_file(filename) }
+        end
+      end
+
+    end
+  end
   # this accelerates translation a tiny bit (halves the time it takes)
   class << self
     alias_method :translate_no_cache, :translate
@@ -6,16 +37,35 @@ module I18n
     LRU_CACHE_SIZE = 2000
 
     def reload!
+      @loaded_locales = []
       @cache = nil
       reload_no_cache!
     end
 
+    LOAD_MUTEX = Mutex.new
+    def load_locale(locale)
+      LOAD_MUTEX.synchronize do
+        return if @loaded_locales.include?(config.locale)
+
+        if @loaded_locales.empty?
+          # load all rb files
+          I18n.backend.load_translations(I18n.load_path.grep(/\.rb$/))
+        end
+
+        # load it
+        I18n.backend.load_translations(I18n.load_path.grep Regexp.new("\\.#{locale}\\.yml$"))
+
+        @loaded_locales << locale
+      end
+    end
+
     def translate(*args)
       @cache ||= LruRedux::ThreadSafeCache.new(LRU_CACHE_SIZE)
       found = true
       k = [args, config.locale, config.backend.object_id]
       t = @cache.fetch(k) { found = false }
       unless found
+        load_locale(config.locale) unless @loaded_locales.include?(config.locale)
         begin
           t = translate_no_cache(*args)
         rescue MissingInterpolationArgument