Hi MarieLouise,
Aside from naming your recordings differently, it is very important that each "word file" is saved separately. From what you described I think you weren't able to duplicate / copy the English word files at all, and that is why your Portuguese edits were saved over the original English ones.
Unfortunately the only way to completely undo your edits is to re-download or re-import your English curriculum. Kindly make sure you save copies of your Portuguese recordings, pictures and videos (if any) in a separate folder or location in your computer before you re-import your English curriculum.
Creating a translation of your Little Reader English Curriculum involves the following steps:
1. Creating new Categories which will contain your translated words
2. Adding your translated words into your new Categories, where you will add in your pre-recorded pronunciations. You can translate words (i.e., word files) in two ways:
Create words from scratch OR edit copies of the English words (using "Save As" when you edit each word).
3. Creating your own Playlist or Course (if you want it like your English course). This step is optional - once you've done Steps 1 and 2, you may already play the lessons for your child.
For detailed instructions, you may refer to this article:
http://support.brillkids.com/entries/20622132-How-can-I-translate-my-Little-Reader-English-Curriculum-into-the-language-I-want-to-teach-P.S.
If you want to delete the course(s) you cloned earlier, just go to TOOLS > Software Information and click on the Delete button for the course you want to remove.