Is it permissible to translate a book that contains beliefs of kufr?

Working in translation is basically permissible, and indeed
there may be some important jobs which it is recommended to do and to meet
the ummah’s need for them. But talking about the translation of a specific
book depends on what this book contains. If the book contains innovations,
misguidance, immorality or kufr, then the translator of this book has a
share in the sin of its author, printer and publisher. But if the book
contains scientific or Islamic or permissible material, then there is
nothing wrong with translating it. 

In our early Islamic history, the translation of the books of
followers of idolatrous religions and heretical philosophy had a far
reaching effect in causing numerous groups of people to go astray from the
guidance of the Qur’aan and Sunnah. This translation began during the year
of the ‘Abbasid caliph al-Ma’moon. 

Al-Maqreezi (may Allah have mercy on him) said: 

Because of al-Ma’moon’s introduction of the books of
philosophy, the philosophical schools of thought became widespread among the
people and the views of various sects, such as the Qadaris, Jahamis,
Mu‘tazilah, Ash‘aris, Karaamis, Khawaarij, Raafidis, Qaraamitah and Baatinis
became so widespread that they filled the earth; there was no group among
them that did not look at philosophy and choose one of its paths to follow.
The trials and tribulations in religion that were brought upon Islam and its
people because of philosophy are indescribable. 

Al-Khutat al-Maqreeziyyah,
2/358 

Based on that, it is not permissible for you to work in
publishing the book mentioned in the question, because publishing it implies
approval of beliefs of kufr and taking part in propagating them, and Islam
warns against cooperating in that which is less serious than that, namely
sin in general terms. Allah says (interpretation of the meaning):

“but do not help one another in sin and transgression”

[al-Maa’idah 5:2]

It should be noted that the ruling we have mentioned applies
if you are translating something to be published and distributed among the
people. But if you are translating that book — or even something that
contains worse kufr — for a Muslim researcher or a study centre so that
these researchers can study the books of these kuffaar in order to refute
them and explain why they are misguided, then there is nothing wrong with
translating those books, so long as those researchers are trustworthy and
you are confident that they will not publish what you have translated for
them. 

You could play a part in spreading Islam by translating good
Islamic books so that they may be published far and wide. You could also
translate books that contain scientific or medical information from other
languages into Arabic. 

And Allah knows best.