We are glad that we can offer our users the ability to translate their apps to other languages, so they can be offered on markets that don't use English as their native language.
To translate any part of the app, please go to Settings → Regional settings → Manage languages. You will get a language interface there that you can use to translate every field visible by your users.
After your language interface opens, click on the Add new button in order to create a new language (name it as you wish). This will give you the ability to translate any portion of the app (or the app builder if you are a reseller).
If you know a specific string that you want to change, then you can use the search option in the top right corner to find it. When you find what you want to translate, you can click on that string, and change it, then click on the little checkmark on the right side to save that change.
After you have changed everything that you wanted, please go to:
Settings -> Regional settings in the app builder again.
You can choose the new language from the dropdown menu in that interface. To complete the procedure click Save on the bottom.
If the application is currently published, you will need to hit the republish button, and those updates should be available to your users on their next application start. The republishing procedure can last up to 15 minutes.