If you exceed your translation limit, you can still translate text in your PDF by installing the free Google Translate app and selecting Translate in the popup menu. Xodo will then open the Google Translate app with your selected text. You can install the Google Translate app from the Google Play Store.
The Google Translate app has a new feature called Tap To Translate, which allows you to access the Google Translate app within other apps, such as Xodo! All you have to do is enable Tap To Translate in your Google Translate app settings and then any time you copy text in Xodo, the popup will appear.
If you would be interested in a paid version of Xodo with more in app translations, please up-vote this idea here: Paid Version of Xodo.