Insert a C# Code in MasterPage - SPO356 P2 PublicFacing Website

Hello,

Is there a way to insert a C# Code that runs on the Server, in a custom MasterPage inSharePoint Office 356 P2?
My goal is to create a Public-Facing Website with multilingual support. (especially two languages)

• The restrictions are: SPO356 P2 doesn't support..
  
• Multilingual Public Facing sites.
  
• Subsites
  
• Meta-Navigation / Navigation-variation

So I decided to solve it with C# code.

Is there a suitable way to do this?

I've tried this following methods:

<% if(somecondition) { %>
   ..some html..<% } %>

or this

<script language="C#" type="text/C#" runat="server">
    private void Submit_onclick(object s, EventArgs e) {
	..some C# Script..
}</script>

both doesn't work. with this error:

Code blocks are not allowed in this file.