Alexander Krylkov

I would recommend C#, particularly Simplify.Web web-framework. C# is easy to start with (especially .NET Core). Simplify.Web is also easy to start with, no extra setup required for simple API, but on the other hand you have power of C# and full control over your API with ability to extend.

Comparing to ASP.NET Core MVC or ASP.NET Core Web API Simplify.Web allows you to easily build your web-site or REST API without any additional/complicated setup, covering cases like localization by default. It's projects structure very lightweight, just a minimum amount of what you need to setup ASP.NET Core request pipeline.

It is build on top of Simplify.DI IOC container abstraction, no dependency on Microsoft.Extensions.DependencyInjection and it's syntax. You can easily switch between DryIoc, SimpleInjector, CastleWindsor etc.

Any internal module of Simplify.Web can be easily replaced on extended by your custom module, covering your custom cases.

For HTML pages generation Simplify.Templates can be used allowing you to use just regular plain HTML without additional setup.

Can be easily integrated with Simplify.WindowsServices converting your web application not just to web-application, but a standalone windows service which can also do some background jobs via Simplify.WindowsServices.

And it is open source, of course :)