How to find which language the app is built? I have to find, which language the app is built on and I have ads data science tips into that.
You can be pretty sure, but you first have to know all the technologies that can output Android APK.

If you know, export the app as an APK and extract it with any zip tool. Then check its content:


If you see 1 class and /assets full of HTML content, then it's likely Phonegap / Cordova
If you see folders named like Appcelerator or Titanium, then it's Titanium Appcelerator
If you see something like a normal Android native structure, then decompile the APK using some online tool. When you do that, you'll be able to see if they used Java only or C++ (if you see a lot of .so files)
If you recognize Kotlin language, then it's Kotlin. You'll see that the code isn't Java
For other technologies, I am not sure but I'm pretty sure there must be something that identifies it.