Edgemaster & shaunmcdonald pointed out that my ad-hoc hackery was

covered by i18n translation framework. So use the magical :count
argument.

Also convert {{size}} to {{count}} in layouts.inbox

app/views/layouts/site.rhtml

@@ -24,7 +24,12 @@
       <% if @user and @user.id %>
         <%= t 'layouts.welcome_user', :user_link => (link_to h(@user.display_name), {:controller => 'user', :action => 'view', :display_name => @user.display_name}, :title => t('layouts.welcome_user_link_tooltip')) %> | 
         <%= yield :greeting %>
-        <%= link_to t('layouts.inbox', :size => @user.new_messages.size), {:controller => 'message', :action => 'inbox', :display_name => @user.display_name}, case @user.new_messages.size when 0 then { :title => t('layouts.inbox_tooltip_0') } when 1 then { :class => 'greeting-bar-unread', :title => t('layouts.inbox_tooltip_1') } else { :class => 'greeting-bar-unread', :title => t('layouts.inbox_tooltip_n', :size => @user.new_messages.size) } end %> |
+        <%
+        inbox_attributes = {}
+        inbox_attributes[:class] = 'greeting-bar-unread' if @user.new_messages.size > 0
+        inbox_attributes[:title] = t 'layouts.inbox_tooltip', :count => @user.new_messages.size
+        %>
+        <%= link_to t('layouts.inbox', :count => @user.new_messages.size), {:controller => 'message', :action => 'inbox', :display_name => @user.display_name}, inbox_attributes %> |
         <%= link_to t('layouts.logout'), {:controller => 'user', :action => 'logout', :referer => request.request_uri}, {:id => 'logoutanchor', :title => t('layouts.logout_tooltip')}%>
       <% else %>
         <%= link_to t('layouts.log_in'), {:controller => 'user', :action => 'login', :referer => request.request_uri}, {:id => 'loginanchor', :title => t('layouts.log_in_tooltip')} %>

config/locales/be.yml

@@ -296,7 +296,7 @@ be:
   layouts:
     welcome_user: "Вітаем, {{user_link}}"
     home: "дамоў"
-    inbox: "уваходныя ({{size}})"
+    inbox: "уваходныя ({{count}})"
     logout: выйсці
     log_in: увайсці
     sign_up: зарэгістравацца

config/locales/de.yml

@@ -324,7 +324,7 @@ de:
   layouts:
     welcome_user: "Willkommen, {{user_link}}"
     home: "home"
-    inbox: "Posteingang ({{size}})"
+    inbox: "Posteingang ({{count}})"
     logout: Abmelden
     log_in: Anmelden
     sign_up: Registrieren

config/locales/en.yml

@@ -335,10 +335,11 @@ en:
     welcome_user_link_tooltip: Your user page
     home: home
     home_tooltip: Go to home location
-    inbox: "inbox ({{size}})"
+    inbox: "inbox ({{count}})"
-    inbox_tooltip_0: Your inbox contains no unread messages
+    inbox_tooltip:
-    inbox_tooltip_1: Your inbox contians 1 unread message
+      zero: Your inbox contains no unread messages
-    inbox_tooltip_n: Your inbox contains {{size}} unread messages
+      one: Your inbox contians 1 unread message
+      other: Your inbox contains {{count}} unread messages
     logout: logout
     logout_tooltip: "Log out"
     log_in: log in

config/locales/fr.yml

@@ -111,7 +111,7 @@ fr:
       comment_from: "Commentaire de {{link_user}} le {{comment_created_at}}"
   layouts:
     welcome_user: "Bienvenue, {{user_link}}"
-    inbox: "Boite aux lettres ({{size}})"
+    inbox: "Boite aux lettres ({{count}})"
     logout: "Déconnexion"
     log_in: "Connexion"
     sign_up: "S'inscrire"

config/locales/he.yml

@@ -297,7 +297,7 @@ he:
   layouts:
     welcome_user: "Welcome, {{user_link}}"
     home: "home"
-    inbox: "inbox ({{size}})"
+    inbox: "inbox ({{count}})"
     logout: logout
     log_in: log in
     sign_up: sign up

config/locales/is.yml

@@ -323,7 +323,7 @@ is:
   layouts:
     welcome_user: "Hæ {{user_link}}"
     home: "heim"
-    inbox: "innhólf ({{size}})"
+    inbox: "innhólf ({{count}})"
     logout: "útskrá"
     log_in: "innskrá"
     sign_up: "búa til aðgang"

config/locales/it.yml

@@ -297,7 +297,7 @@ it:
   layouts:
     welcome_user: "Benvenuto, {{user_link}}"
     home: "posizione iniziale"
-    inbox: "in arrivo ({{size}})"
+    inbox: "in arrivo ({{count}})"
     logout: esci
     log_in: entra
     sign_up: iscriviti

config/locales/nl.yml

@@ -297,7 +297,7 @@ nl:
   layouts:
     welcome_user: "Welkom, {{user_link}}"
     home: "home"
-    inbox: "Postvak IN ({{size}})"
+    inbox: "Postvak IN ({{count}})"
     logout: uitloggen
     log_in: inloggen
     sign_up: registreren

config/locales/pl.yml

@@ -300,7 +300,7 @@ pl:
   layouts:
     welcome_user: "Witaj, {{user_link}}"
     home: "główna"
-    inbox: "skrzynka ({{size}})"
+    inbox: "skrzynka ({{count}})"
     logout: wyloguj
     log_in: zaloguj się
     sign_up: zarejestruj

config/locales/ru.yml

@@ -297,7 +297,7 @@ ru:
   layouts:
     welcome_user: "Добро пожаловать, {{user_link}}"
     home: "домой"
-    inbox: "входящие ({{size}})"
+    inbox: "входящие ({{count}})"
     logout: выйти
     log_in: войти
     sign_up: регистрация

config/locales/sl.yml

@@ -326,7 +326,7 @@ sl:
   layouts:
     welcome_user: "Dobrodošli, {{user_link}}"
     home: "domov"
-    inbox: "prejeta pošta ({{size}})"
+    inbox: "prejeta pošta ({{count}})"
     logout: odjava
     log_in: prijava
     sign_up: vpis

config/locales/zh-CN.yml

@@ -295,7 +295,7 @@ zh-CN:
   layouts:
     welcome_user: "Welcome, {{user_link}}"
     home: "home"
-    inbox: "inbox ({{size}})"
+    inbox: "inbox ({{count}})"
     logout: logout
     log_in: log in
     sign_up: sign up