Hi! I saw your website, was done with ASP.NET Web Forms (ASPX), that is 1996 techonology.
If you really want to outstand on SEO, the recommendation will be to port it to C# ASP.NET Core 2.2, that's the fastest framework out there, SEO cares about loading time.
You can check by yourself the difference between ASP.NET Web Forms and ASP.NET Core is like day and night.
Problem is the budget wont allow us to do that, as this will be a massive undertaken.
Of course during that work, we can use Localization so you have it in 2 languages
Thanks!
Felice
PD: ASP.NET Core is still C# in Visual Studio 2017, just a different kind of Server Side and HTML Rendering