use {{count}} instead of {{sent_count}} so rails plural forms will kick in

app/views/message/outbox.html.erb

@@ -1,6 +1,6 @@
 <h2><%= t'message.outbox.my_inbox', :inbox_link => link_to(t('message.outbox.inbox'), url_for(:controller => "user", :action => "inbox", :id => @user.display_name)) %>/<%= t'message.outbox.outbox' %></h2>
 
-<p><%= t'message.outbox.you_have_sent_messages', :sent_count => @user.sent_messages.size %>
+<p><%= t'message.outbox.you_have_sent_messages', :count => @user.sent_messages.size %>
 
 <% if @user.sent_messages.size > 0 %>
   <div id="messages">

config/locales/af.yml

@@ -335,7 +335,7 @@ af:
       outbox: Posvak UIT
       subject: Onderwerp
       to: Aan
-      you_have_sent_messages: U het {{sent_count}} gestuurde boodskappe
+      you_have_sent_messages: U het {{count}} gestuurde boodskappe
     read: 
       date: Datum
       from: Van

config/locales/be.yml

@@ -367,7 +367,7 @@ be:
       subject: Тэма
       title: Зыходныя
       to: Каму
-      you_have_sent_messages: У вас {{sent_count}} дасланых паведамленняў
+      you_have_sent_messages: У вас {{count}} дасланых паведамленняў
     read: 
       back_to_inbox: Вярнуцца да ўваходных
       back_to_outbox: Вярнуцца да зыходных

config/locales/br.yml

@@ -471,7 +471,7 @@ br:
       subject: Danvez
       title: Boest kas
       to: Da
-      you_have_sent_messages: Kaset hoc'h eus {{sent_count}} kemennadenn
+      you_have_sent_messages: Kaset hoc'h eus {{count}} kemennadenn
     read: 
       back_to_inbox: Distreiñ d'ar voest resev
       back_to_outbox: Distreiñ d'ar voest kas

config/locales/de.yml

@@ -439,7 +439,7 @@ de:
       subject: Betreff
       title: Gesendet
       to: An
-      you_have_sent_messages: Du hast {{sent_count}} Nachrichten versendet
+      you_have_sent_messages: Du hast {{count}} Nachrichten versendet
     read: 
       back_to_inbox: Zurück zum Posteingang
       back_to_outbox: Zurück zu Gesendete Nachrichten

config/locales/en.yml

@@ -581,7 +581,7 @@ en:
       my_inbox: "My {{inbox_link}}"
       inbox: "inbox"
       outbox: "outbox"
-      you_have_sent_messages: "You have {{sent_count}} sent messages"
+      you_have_sent_messages: "You have {{count}} sent messages"
       to: "To"
       subject: "Subject"
       date: "Date"

config/locales/es.yml

@@ -464,7 +464,7 @@ es:
       subject: Asunto
       title: Salida
       to: A
-      you_have_sent_messages: Tienes {{sent_count}} mensajes enviados
+      you_have_sent_messages: Tienes {{count}} mensajes enviados
     read: 
       back_to_inbox: Regresar a la bandeja de entrada
       back_to_outbox: Regresar a la bandeja de salida

config/locales/fi.yml

@@ -383,7 +383,7 @@ fi:
       subject: Otsikko
       title: Lähetetyt
       to: Vastaanottaja
-      you_have_sent_messages: Sinulla on {{sent_count}} lähetettyä viestiä
+      you_have_sent_messages: Sinulla on {{count}} lähetettyä viestiä
     read: 
       back_to_inbox: Takaisin saapuneisiin
       back_to_outbox: Takaisin lähetettyihin

config/locales/fr.yml

@@ -444,7 +444,7 @@ fr:
       subject: Objet
       title: Boîte d'envoi
       to: À
-      you_have_sent_messages: Vous avez envoyé {{sent_count}} messages
+      you_have_sent_messages: Vous avez envoyé {{count}} messages
     read: 
       back_to_inbox: Revenir à la boîte de réception
       back_to_outbox: Revenir à la boîte d'envoi

config/locales/hsb.yml

@@ -468,7 +468,7 @@ hsb:
       subject: Temowe nadpismo
       title: Pósłany
       to: Komu
-      you_have_sent_messages: Sy {{sent_count}} pósłanych powěsćow
+      you_have_sent_messages: Sy {{count}} pósłanych powěsćow
     read: 
       back_to_inbox: Wróćo k póstowemu kašćikej
       back_to_outbox: Wróćo k pósłanym powěsćam

config/locales/hu.yml

@@ -474,7 +474,7 @@ hu:
       subject: Tárgy
       title: Elküldött üzenetek
       to: Címzett
-      you_have_sent_messages: "{{sent_count}} elküldött üzeneted van"
+      you_have_sent_messages: "{{count}} elküldött üzeneted van"
     read: 
       back_to_inbox: Vissza a beérkezett üzenetekhez
       back_to_outbox: Vissza az elküldött üzenetekhez

config/locales/is.yml

@@ -475,7 +475,7 @@ is:
       subject: Titill
       title: Úthólf
       to: Til
-      you_have_sent_messages: Þú hefur sent {{sent_count}} skeyti
+      you_have_sent_messages: Þú hefur sent {{count}} skeyti
     read: 
       back_to_inbox: Aftur í innhólf
       back_to_outbox: Aftur í úthólf

config/locales/it.yml

@@ -330,7 +330,7 @@ it:
       subject: Oggetto
       title: In uscita
       to: A
-      you_have_sent_messages: Hai {{sent_count}} messaggi inviati
+      you_have_sent_messages: Hai {{count}} messaggi inviati
     read: 
       back_to_inbox: Ritorna ai messaggi in arrivo
       back_to_outbox: Ritorna ai messaggi in uscita

config/locales/ja.yml

@@ -411,7 +411,7 @@ ja:
       subject: タイトル
       title: 送信箱
       to: 宛先
-      you_have_sent_messages: "{{sent_count}}この送信済みメッセージがあります"
+      you_have_sent_messages: "{{count}}この送信済みメッセージがあります"
     read: 
       back_to_inbox: 受信箱に戻る
       back_to_outbox: 送信箱に戻る

config/locales/ko.yml

@@ -309,7 +309,7 @@ ko:
       people_mapping_nearby: 근처를 지도 입력한 사람들
       subject: 제목
       title: 보낸 쪽지함
-      you_have_sent_messages: "{{sent_count}} 개의 쪽지를 보냈습니다."
+      you_have_sent_messages: "{{count}} 개의 쪽지를 보냈습니다."
   notifier: 
     diary_comment_notification: 
       banner1: "*                         이 email에 답장하지 마세요.                          *"

config/locales/nl.yml

@@ -454,7 +454,7 @@ nl:
       subject: Onderwerp
       title: Postvak UIT
       to: Aan
-      you_have_sent_messages: U hebt {{sent_count}} verzonden berichten
+      you_have_sent_messages: U hebt {{count}} verzonden berichten
     read: 
       back_to_inbox: Terug naar Postvak IN
       back_to_outbox: Terug naar Postvak UIT

config/locales/no.yml

@@ -433,7 +433,7 @@
       subject: Emne
       title: Utboks
       to: Til
-      you_have_sent_messages: Du har sendt {{sent_count}} meldinger
+      you_have_sent_messages: Du har sendt {{count}} meldinger
     read: 
       back_to_inbox: Tilbake til innboks
       back_to_outbox: Tilbake til utboks

config/locales/pl.yml

@@ -337,7 +337,7 @@ pl:
       subject: Temat
       title: Wiadomości wysłane
       to: Do
-      you_have_sent_messages: Wysłaleś/aś {{sent_count}} wiadomości
+      you_have_sent_messages: Wysłaleś/aś {{count}} wiadomości
     read: 
       back_to_inbox: Powrót do wysłanych
       date: Nadano

config/locales/pt-BR.yml

@@ -458,7 +458,7 @@ pt-BR:
       subject: Assunto
       title: Caixa de Saída
       to: Para
-      you_have_sent_messages: Você tem {{sent_count}} mensagens enviadas
+      you_have_sent_messages: Você tem {{count}} mensagens enviadas
     read: 
       back_to_inbox: Voltar para a caixa de entrada
       back_to_outbox: Voltar para a caixa de saída

config/locales/ru.yml

@@ -471,7 +471,7 @@ ru:
       subject: Тема
       title: Исходящие
       to: Кому
-      you_have_sent_messages: Вы отправили {{sent_count}} сообщений
+      you_have_sent_messages: Вы отправили {{count}} сообщений
     read: 
       back_to_inbox: Назад ко входящим
       back_to_outbox: Назад к исходящим

config/locales/sl.yml

@@ -452,7 +452,7 @@ sl:
       subject: Zadeva
       title: Poslana pošta
       to: Za
-      you_have_sent_messages: Poslali ste {{sent_count}} sporočil
+      you_have_sent_messages: Poslali ste {{count}} sporočil
     read: 
       back_to_inbox: Nazaj na prejeto pošto
       back_to_outbox: Nazaj na poslano pošto

config/locales/vi.yml

@@ -474,7 +474,7 @@ vi:
       subject: Tiêu đề
       title: Hộp thư đã gửi
       to: Tới
-      you_have_sent_messages: Bạn đã gửi {{sent_count}} thư
+      you_have_sent_messages: Bạn đã gửi {{count}} thư
     read: 
       back_to_inbox: Trở về hộp thư đến
       back_to_outbox: Trở về hộp thư đã gửi

config/locales/yo.yml

@@ -65,7 +65,7 @@ yo:
     welcome_user: Kabo, {{user_link}}
   message: 
     outbox: 
-      you_have_sent_messages: O ni {{sent_count}} sent messages
+      you_have_sent_messages: O ni {{count}} sent messages
     read: 
       back_to_inbox: Pada si inbox
       back_to_outbox: Pad si outbox

config/locales/zh-CN.yml

@@ -332,7 +332,7 @@ zh-CN:
       people_mapping_nearby: 在您附近的人
       subject: 主体
       to: 给
-      you_have_sent_messages: 您有{{sent_count}} 已发送邮件
+      you_have_sent_messages: 您有{{count}} 已发送邮件
     read: 
       back_to_inbox: 返回收件箱
       back_to_outbox: 返回发件箱

config/locales/zh-TW.yml

@@ -459,7 +459,7 @@ zh-TW:
       subject: 主旨
       title: 寄件匣
       to: 收件者
-      you_have_sent_messages: 您有 {{sent_count}} 個寄送的訊息
+      you_have_sent_messages: 您有 {{count}} 個寄送的訊息
     read: 
       back_to_inbox: 回到收件匣
       back_to_outbox: 回到寄件匣