Google Translate just added a very useful one feature on Android. The 'Tap to Translate' feature allows you to use text translation from within any app.
For example, when you copy a text from WhatsApp, the Translation bubble will appear. So you can do click there to see the translated text.
From the same point you can also change the languages or make a new translation.
Meanwhile, iOS users will have Android's Offline mode. Offline mode will do shorter translations without needing to connect to the internetnetwork or mobile data connections such as Google Translate.
You should download language packs that are around 25MB each.
As Google reports, packet size has been reduced by 90%. You can enable offline languages by clicking the arrow next to their name languages.