Hi Machu, we've discussed the same question in the LR v3 thread earlier:
http://forum.brillkids.com/announcements/update-to-little-reader-v3!/msg92254/#msg92254
Right now it's not possible to copy your English courses and translate directly from the Courses view, because doing so will edit the original content, which you do not want to happen.
What we recommend is to copy the categories and the words in them, and translate those from the Play & Edit > Categories screen. Once you're done with translating all your categories, you can go back to the Courses section and create a new course.
You may refer to this article for details on how you can translate the categories and words:
http://support.brillkids.com/entries/20622132-how-can-i-translate-my-little-reader-english-curriculum-into-the-language-i-want-to-teachI had one more idea, is it possible to edit original Semesters (also media file names and everything) and then again download original Semesters, so I'll have edited original semester (translated) and non-edited original (english)?
Yes, this is possible as long as you've renamed the word file names for your translated words. You will see the file name of each word in Edit Word > Others. If you edit the English words directly without changing the words' file names, your edits will be overwritten once you import your original content files.
If the duplication I ask for was not possible and I decided to sacrifice english original and edit it (translate), is it then possible to export the edited Semester to the second computer, also with licensed version of Little Reader? (using export tool or by manual file replacement in Windows)
Again, you need to make sure that you change the word file name for your translated words so you can have both the original and the translated content in your LR.
We'll look into adding a new function which can help clone courses for translating without changing the original courses, but this may not be available any time soon. In the meantime, the best way is what we've recommended above.