Once copyright registration has been filed, does a separate copyright need to be obtained if original book is reprinted by copyright owner in another language?
I'm not a lawyer, but in the absence of anyone else answering so far, here's my view.
A translation of a book is a derivative work from the book in the original language. But it is ALSO a separate work from the book in the original language.
For a person to translate a copyrighted work without the original owner's permission is definitely a violation of copyright. There have been many cases where authors have successfully sued those who made pirate translations in an attempt to beat the authorised translation of a bestselling book into print and profit from doing that.
So in that sense, the original copyright owner automatically retains ownership and doesn't have to do anything more to assert that ownership. No one can legally claim that an unauthorized translation "doesn't count" as copyright violation just because the same story is put into a different language.
However the authorised translation is also a work in its own right. The work of translating involved skill and effort. The translation is separate from the original and has its own copyright. If the law where you are requires you to do something to register copyright for each work, then you should register the translation as well as the original.
If the book is translated into multiple languages, all the above applies to each translation.
Maybe you are just asking out of curiosity, but if there are significant bad consequences for getting this wrong, I strongly advise you to check with a copyright lawyer in your own country / jurisdiction.