Google Talk still works with XMPP so you can use Pidgin and there is an official tutorial Configure Pidgin to connect to Google Talk
But there is missing important part: you’ll get «Not Authorized» error during connect.
The problem is that Google tries to improve security so your Google/Gmail password ideally should never be entered anywere except of Google itself so no any trojan or virus can’t stole your password.
So how can you login into Google Talk without inputting a password from Google Account?
Well, you can generate another password.
Go to My Account, and in the «Sign-in & Security» column, go to Signing in to Google and then App passwords
You’ll see the «Select the app and device you want to generate the app password for.»
Select App: Mail
Select Device: Other
Then input «pidgin»
Press Generate button
Then you’ll see «Your app password for your device»
Copy the generated password and input it into Pidgin account and that’s it.