I'm not entirely sure what the question is. Are you asking what language is getting used by the server on the receiving end of the URL request? If that's what you're asking, the Insert From URL script step doesn't care.
What I want to do is use insert url for APIs
Each API based website has its own link to use
And those websites usually give examples for each language
After doing some trials (using the wxamples that they give), I manage to figure out the link
What you're looking for in API documentation is what the resulting URL looks like, instead of the terms each languages uses to generate it. If the API documentation includes it, the documentation for cURL is the best place to start because it exposes the URL you'd need to make in FileMaker the most directly.
APIs may return different kinds of TEXT:
The underlying application used doesn't matter, but the results (if needed to be processed for consumption by FM) depends on what's available and how you are able to process. FM eats TEXT for breakfast. LOL
Heed jbante's advice and get the API documentation to learn your options for sending and receiving. Some may require secure connections & authenticated access. Some may require a cycle of: request-response-request-result and a single URL may not work, so a plug-in or other means external to FM would be employed.