You can change or translate the "Confirm" button text in questions using the XLIFF export function.
The following steps detail this process. In this example we will update the Confirm Button to show a French translation
1. From the Course Structure view select Translation Export (XLIFF) in the Actions dropdown
2. That will download a zip file containing XLIFF files for each topic and another one called localization-localization.xliff which contains text elements common to all topics, including the Confirm text.
3. Extract the localization-localization.xliff file from the zip. This will save a copy to your desktop/laptop
4. You can either use an XLIFF editor (there are some free Open Source ones available) or you can simply open it up in a text editor.
5. Use CTRL + F and search for Confirm
6. Update the Confirm text in the <target> field with the translation
7. Save the change
8. Upload that file back into your course using the Translation Import (XLIFF) option in the Actions dropdown
9. When you preview the course in the French, the Confirm button will be updated