If at all you wish to have a conversation with another person who speaks a different language. (Say you speak english and the person at the other end speaks Portuguese), you have to open another tab and then open the Google translator. It would be very difficult for you to get the language translated this way. Let me tell you an easy way for this.
You can add bots in your hangouts. These bots are like persons on the other side of the computer. For example, I you use the spanish bot, when you enter english word HELLO, you will be replied with HOLA.
How to add these bots.
Once you open the hangout section in Gmail, go to search bar upon the hangouts and then use tis format to choose the bot.
(From language)2(To language)@bot.talk.google.com
Eg: If you want to use an English Portuguese bot, type this.
Then Invite the bot.
For other languages codings, see here
That's all. Now you need not open a new tab and get the texts translated. All the translations can be done by the bot inside the hangouts itself.