I have an android app: plain text, and I want to make it interactive:
on clicking the word, I want a window to pop up and show the translation of the word
Probably i should use some sort of Google Translate API
please tell me, what direction should i head digging in order to develop such an app
For Google Translate you should look into the Google Translate Api docs on developers.google.com.
It isn’t free though, Google Translate is a paid service that costs $20 per 1 million characters.
You can use Google Translate for free but that is stealing and would be unadvisable, especially if you want to publish your app on the Play marketplace.
Microsoft offer a free Bing Translation Api. It’s free up to 2 million characters per month. If you combine that with a caching system so you don’t constantly hit it for words already translated then it should work fine.