Sure, APIs are written in many languages. JSON is just a format for data exchange, bunch of nested brackets etc.

I recommend the site learnxinyminutes.com -- great resource for a quick look at the syntax and major features of languages. Here's the page for JSON, in fact: https://learnxinyminutes.com/json/

Holy gracious sakes... I am sorry, but I have no idea why the person suggests you Python over JavaScript at this point...

Python is not only uncommon in syntax if compared to almost anything else popular, but also slow for web-dev just if you;d comapred its Jit to PHP or JavaScript's runtimes even.

There's so much out there already online discussed and compared with... Why... do people just don't care about others' time with baseless questions and require others to step up and invest their time into in hope to support them to not make a yet another mistake...

Again... Python... for web? Yes, it's a great programming language for scripts (though I do still prefer Bash, Perl, JavaScript, and PHP, if we consider interpretable scripts only), and there's Django and such, but... please do consider and compare the unique syntax, lack of proper accessibility scopes (e.g. private, public variables, without additional support/workarounds as conventions), speed and, more importantly, maintainability for teamwork and in personal life even, with other programming language for frameworks...

Of course, not. No, Python would not be okay at all as a first language for web-dev. Please do consider a language that is C-like and is comprehensible, with modules and adequate packaging with at least pinnable dependencies which is not supported by the common package managers for Python at all.

Please do consider actually strictly typed languages, or least as strict as PHP at this point.
There are ineffably magnificent guide books for it, and the programming language as PHP is dated enough to find any Community to support if ever required. Frameworks like Laravel and Symfony are used by marvelous vendors, and you'll get the idea who enterprise projects work. Valve's Steam even uses PHP.

Not sure what you meant by "JSON API" in this thread, but just in case:
- https://laravel.com/docs/13.x/eloquent-resources#jsonapi-resources
- https://laravel.com/learn/php-fundamentals/why-php
- https://laravel.com/docs/13.x/installation#why-laravel
- https://symfony.com/why-use-a-framework

In case of JavaScript, I cannot suggest you the most precise, since I don't know you. Every course should be approached subjectively I believe, since you have a different worldview, perspective, life and development experience. Why do you ask anyone such a question? Do you know these people to trust the answer even?
What does "best" mean even?

Where to start? Do you need to cover the object-based vs object-oriented programming?
Do you want to know differences between NodeJS and common browsers (e.g. at nodejs.org)?
Do you need to cover up specific JavaScript ECMA 232 subject - ECMAScript?
Do you have questions regarding JavaScript engines like V8?
What is it exactly you have issue with to focus on?

Objectively, there are few references that are popular in fairly adequate places, and I would definitely recommend to start from those, too:
- Eloquent JavaScript, 3rd Edition (book);
- You Don't Know JS Yet (book);
- JavaScript - Laracasts;
- Learn JavaScript Online;
- Lightning Fast Builds w/ Vite - Vue Mastery...

Just in case, if you find the first two books mentioned interesting, you may also find the following special/marvelous, too:
- Programming JavaScript Applications by Eric Elliott;
- High Performance JavaScript by Nicholas C. Zakas;
- Functional JavaScript by Michael Fogus;
- The Definitive Guide by David Flanagan;
- Effective JavaScript by David Herman.

Have you checked out already?:
- 1. Server-side rendering (SSR) subjects;
- 2. Static-site generator subjects;
- 3. Scrapers like Webscrapbook...

If you want something more restrictive, please consider languages with a compiler which are used for web-dev as:
- Go: https://go.dev/solutions/webdev
- Rust: https://rust-lang.org/what/wasm/

I've been around 20 years into the web-development... and I still have no idea why people ask questions, listen to 1-2 answers, and start their learning from a start that may not match their requirements nor subjective worldviews...

Please do consider reading about the current trends, benchmarks, the most common issues, and the main use of the languages out there...

Or, please do ask actually valuable questions, which will save yours precious, finite, treasured life time, too...