Completa i18n IT/EN/FR/DE/ES su sito pubblico, area autenticata e admin.

Tutte le view marketing, legali, viewer, dashboard e admin usano t(); mailer utente-facing e flash localizzati; admin con LocaleResolver e selettore lingua.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/controllers/admin/billing_invoices_controller.rb

@@ -8,7 +8,7 @@ module Admin
     end
 
     def new
-      redirect_to admin_billing_path(club_id: @club.id), alert: "Carica il PDF dalla lista «Pagamenti da fatturare»."
+      redirect_to admin_billing_path(club_id: @club.id), alert: t("admin.flash.invoice_upload_hint")
     end
 
     def create
@@ -18,7 +18,7 @@ module Admin
 
       if @invoice.save
         redirect_to edit_admin_club_billing_invoice_path(@club, @invoice),
-                    notice: "Bozza creata. Carica il PDF dalla pagina Fatturazione o qui sotto."
+                    notice: t("admin.flash.invoice_draft_created")
       else
         @payment = @invoice.billing_payment
         flash.now[:alert] = @invoice.errors.full_messages.join(", ")
@@ -36,9 +36,9 @@ module Admin
       if issuing?
         Billing::IssueInvoice.call(invoice: @invoice, pdf: params.dig(:billing_invoice, :pdf))
         redirect_to admin_billing_path(club_id: @club.id),
-                    notice: "Fattura #{@invoice.number} emessa e inviata a #{@club.billing_email}."
+                    notice: t("admin.flash.invoice_issued", number: @invoice.number, email: @club.billing_email)
       elsif @invoice.save
-        redirect_to admin_billing_path(club_id: @club.id), notice: "Fattura #{@invoice.number} aggiornata."
+        redirect_to admin_billing_path(club_id: @club.id), notice: t("admin.flash.invoice_updated", number: @invoice.number)
       else
         @payment = @invoice.billing_payment
         flash.now[:alert] = @invoice.errors.full_messages.join(", ")
@@ -61,7 +61,7 @@ module Admin
     end
 
     def issuing?
-      params[:commit].to_s == "Emetti e invia via email"
+      params[:commit_action].to_s == "issue"
     end
 
     def invoice_params