You can add the texts in the new language by accessing the Panel Translations.
You can access the panel translations from the edit bar of the App Multilingual. Click on the icon Flag.
From the Translations, in the top you can select which languages to display in order to have a reference of the content that's already there. By clicking on the text fields, you can begin to add the translation in the appropriate language.
If you want to maintain the formatting style of the text already present, click on the text field to the left and the arrow icon. In this way, it will be imported the original formatting.
After you have added and modified the text, click the Save button.