All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Lahore Ahmadiya movement is a group belonging to the Qadiyani cult which is known for its disbelief and deviation. It has some differences from Qadiyanism. We have issued some Fataawa concerning Qadiyanism, see the Fataawa 88413 and 86488.
So, it is not allowed to translate their books since it is spreading falsehood and cooperating in its propagation. Allaah Says (which means): {And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allaah; indeed, Allaah is severe in penalty.}[Quran 5:2].
The Prophet said: "Whoever calls to deviation will have (the burden of sin upon him) like the sins of those who follow him, without their sins being mitigated thereby in the least." [Muslim]
Translating their books is actually calling to their deviation, so it is compulsory to refrain from translating them.
Allaah Knows best.