thrown into a backend project as a backend dev with a language I don't know, how fucked am I?

If you've firmly but politely articulated what your skill set is, and they've told you it's fine, you're literally being paid to skill up. I don't see the problem. You haven't lied about your qualifications, instead you've been told they want you on the project, even though you don't know the language yet. This is a good thing.

This doesn't feel like a disaster to me at all. This is an opportunity to grow and learn new things and new ways of doing things. It looks like your environment is very supportive and understanding that it will take some time and effort to get up to speed and are offering mentoring. And businesses often have valid technical or non-technical reasons for using a particular software stack - for example C# developers are likely easier to find than C++ developers which makes hiring easier in the future.

My suggestion is to take some deep breaths reset your perspective. Yes, sometimes it's not fun to push outside of your comfort zone, and it sounds like that is creating a lot of anxiety for you, but you'll do fine. This is very similar to how I got started professionally programming 25 years ago.

What do you mean? Your team says they're going to help you learn as you go. I think you'll be fine. Be proactive when asking questions, you'll be fine! Just set expectations. Make sure your manager knows you don't know this language and tell them you can learn as you go with assistance but you'll need some time before you're very productive.

If you can code in C++ you should be able to muddle through in C# no problem. The runtime will help prevent the worst SNAFUs; y'know, pointer errors (there are none, unless you use the unsafe block or p/invoke), memory leaks etc. Just look at the existing code and cargo-cult it til you make it. You got this. :)

If you have "some hobbyist experience" with C++, then you should definitively avoid it and go with C#.

You should be at least "C++ is a landmine, be careful there" tall before allowed to play with it alone.

Other team members already being familiar with the other alternative makes it a better bet already. Besides, C# is fairly nice, it's arguably much easier to learn than C++, C# and similarly (or more) high-level languages have been focused more than C++ in a lot of education, etc.

C++ is a worse idea, it is not a good web backend language.

C# is pretty easy. As long as your boss doesn't expect you to magically already be good at the thing they refused to allocate time for you to train in, you probably can just start trying to glue bits of C# web API examples together as your first project.

Have you used Java before? It's not a big leap from Java to C#, most of the concepts are the same. At least C# is a memory safe language, although I'm not sure if you're unfamiliar with the code base and languages if it really makes a difference which language you use here. Hopefully your coworkers can help hold your hand a bit here, this situation sucks.

It's not a fucked up situation. I'm a Ruby developer and I got hired in a Scala shop with no experience. It took just a couple weeks to get up to speed and everyone was understanding.

Since you know programming principles already, the difference between languages is mostly in their APIs. But even experienced developers spend half their time reading docs about APIs. It's nothing out of the ordinary.

I would say C# is a better bet as it abstracts a lot more from you than cpp. And as the name suggests the syntax is much like C so if you already have some basic understanding you should be fine. Also as others have said you'd is a learning opportunity, try to have fun with it!

C# isn't that difficult to learn. Don't be overwhelmed by languages or frameworks, they aren't so different from each other.

Tell me you are employed by an Italian IT company without telling me you are employed by an Italian IT company. While reading "I will learn on the field" it reminded me of my previous employer who was very fond of this "learning on the job" approach. To the clients' detriment who had their expensive software developed by inexperienced programmers.

A good developer doesn't need to worry themselves over the language used. For the most part programming principles are universal, besides Object Oriented vs Functional programming languages. Since you're not moving from, say, Java to Elixir, you should be fine.

C# isn't too complicated tbh. A lot of things are done for you i.e. memory management.

Honestly if you're not a cpp pro that seems like it would go worse as there are so many ways to shoot yourself in the foot.

You should be able to learn c# as you go.

ChatGPT is a great resource for this. If you paste in a snippet and ask it to explain you'll get a decent answer with enough context for follow up questions or things to Google.

You can also ask it to explain how to do things. As long as it's pretty general.

Getting paid to learn is always great in my experience.

If I would complain about any new language or environment I'd be dropped in, I'd probably in the loony bin by now.

Tell the team leader that you don't know the language but are willing to learn, read the existing code which will give you a feel for the language, the project, and the local programming style, all in one go, and you should be fine. Imagine the backend was written in PL/I, Prolog, or LISP instead of just another ALGOL dialect ;-)

If you've been working the front end, you know what the backend is supposed to provide, so you might have been picked because see you as a domain expert. Don't be surprised if you end up acting as a leader in that regard.

And C# isn't that hard. I earned my living with Visual Basic, Access, and VBA until thrown into a C# job. Other than the damned braces and semicolons, it wasn't that big a deal.

Do you / can you work from home? If so, outsource to India for 1/10 the costs, stay home and chill, keep the difference.

What language are you familiar with? Switching between the C-style OOP languages is honestly pretty straightforward.

Depending on the (API) complexity and speed requirements it might be useful to start by implementing in plain old C. Easy enough to add on class structures later (i.e. transcode to either of those options) if needed. Also consider Rust, as long as you're going to learn something, it'd be nice if it was current and forward facing.

system.out.you.are.fucked()

You have copilot? You'll be fine if so, just throw down comments for what you want it to do and tweak it when it doesn't compile.