How to add Google Talk (~ Hangouts) to Pidgin chat client?
There is a hangups plug-in, which supports (if I understand correctly) Google Talk (~ Hangouts). How do I add it to my Pidgin chat client?
This is a comprehensive step-by-step guide on
How to compile and install Pidgin and make it work with Google Talk (~ Hangouts) on Linux :
The differences between Hangouts and Google Talk you will find on this page:
https://support.google.com/a/answer/4564211
1. Enable 2-Step Verification on this page:
https://accounts.google.com/SmsAuthConfig 
2. Generate a new App password for Pidgin on this page, select Other and name it however:
https://security.google.com/settings/security/apppasswords 
3. Install the latest version of Pidgin for your system from this page:
https://pidgin.im/download/ or from repository of your Linux distribution or compile it from source (or for Max OS X they recommend using http://adium.im/)
4. To avoid security bugs, you should often check if your Linux distribution repository contains the latest version available, which you may check on this page https://pidgin.im/news/security/
5. If you choose to compile, you simply install the dependencies, download and compile the code, and install Pidgin as follows:
$ sudo apt-get build-dep pidgin
$ sudo apt-get source pidgin
$ tar xjvf pidgin-2.x.y.tar.bz2
$ cd pidgin-2.x.y
$ ./configure && make && sudo make install
Alternately, eg on Debian, where you (by default) have to su instead of sudo (haven't tested myself, correct me if I'm wrong):
$ su -
# apt-get build-dep pidgin
# apt-get source pidgin
# exit
$ tar xjvf pidgin-2.x.y.tar.bz2
$ cd pidgin-2.x.y
$ ./configure && make
$ su -
# make install
If it fails for some reason, please refer to this page:
https://developer.pidgin.im/wiki/Installing%20Pidgin#WhycantIcompilePidgin
6. Right-click the system-tray icon of Pidgin and choose Accounts.
7. Add or modify your Google Talk account to have Username without @gmail.com or your own domain.
8. If you have your own domain for Google account, fill in the Domain field, otherwise there should be gmail.com present by default (without @).
9. The Resource is an XMPP specific thing that allows one to use several clients for the same account. Under normal circumstances leave blank.
10. Fill in the Password generated in step two.
11. Optional, but convenient, if on a secure computer, is ticking Remember password.
12. Local alias leave blank.
13. It should look like this: 
14. On Advanced tab make sure you have Require encryption chosen and disabled plaintext.
15. Note, that after you save these settings, the protocol will automatically change to XMPP, which is currently available to third-party applications like Pidgin.