(18:56) And We send not the messengers except as bringers of good tidings and warners. And those who disbelieve dispute by [using] falsehood to [attempt to] invalidate thereby the truth and have taken My verses, and that of which they are warned, in ridicule.
Muhammad Taqi-ud-Din al-Hilali and Muhammad Muhsin Khan,
(18:56) And We send not the Messengers except as giver of glad tidings and warners. But those who disbelieve, dispute with false argument, in order to refute the truth thereby. And they treat My Ayat (proofs, evidences, verses, lessons, signs, revelations, etc.), and that with which they are warned, as jest and mockery!
Mohammed Marmaduke William Pickthall
(18:56) We send not the messengers save as bearers of good news and warners. Those who disbelieve contend with falsehood in order to refute the Truth thereby. And they take Our revelations and that wherewith they are threatened as a jest.
Abdullah Yusuf Ali
(18:56) We only send the messengers to give Glad Tidings and to give warnings: But the unbelievers dispute with vain argument, in order therewith to weaken the truth, and they treat My Signs as a jest, as also the fact that they are warned!
Mohammad Habib Shakir
(18:56) And We do not send apostles but as givers of good news and warning, and those who disbelieve make a false contention that they may render null thereby the truth, and they take My communications and that with which they are warned for a mockery.
(18:56) And in no way do We send the Emissaries except as constant bearers of good tidings and constant warners; and the ones who have disbelieved dispute with untruth that they may rebut thereby the Truth. And they have taken to themselves My signs and what they are warned of in mockery.
(18:56) We send the Messengers (not as bearers of punishment) but as bearers of glad tidings (of prosperity in return for faith and righteousness) and warners (against the evil consequences of misguidance). Whereas those who disbelieve contend on the basis of falsehood in order to refute the truth thereby; and they take My Revelations and that (the punishment) of which they are warned in mockery.
Amatul Rahman Omar
(18:56) And We send no Apostles but as Bearers of good tidings (to the obedient on the one hand) and as Warners (to the disobedient on the other). And those who disbelieve contend by means of falsehood that they may refute the truth thereby. And they scoff at My commandments and (the punishment) of which they had been warned.
(18:56) And We do not send the messengers except (as) announcers of good news and warners/givers of notice, and those who disbelieved argue/dispute with/by the falsehood to nullify with it the truth , and they took My verses/evidences and what they were warned/given notice (with it) mockingly/making fun.
(18:56) We never send apostles but to convey happy tidings, and to warn. But those who disbelieve contend with false arguments to nullify the truth. They make a mockery of My revelations and of what they had been warned.
A. J. Arberry
(18:56) And We send not the Envoys, but good tidings to bear, and warning. Yet do the unbelievers dispute with falsehood, that they may rebut thereby the truth. They have taken My signs, and what they are warned of, in mockery.
Abdul Majid Daryabadi
(18:56) And We send not apostles save as bringers of glad tidings and warners; and those who disbelieve dispute with falsehood that they rebut thereby the truth; and they take My signs and that whereof they are warned as a mockery.
Maulana Mohammad Ali
(18:56) The only reason for Our sending the Messengers is to give the human being the glad news of Our mercy and to warn him about Our wrath. The disbelievers argue by false means to refute the Truth. They mock My miracles and warnings.
Hamid Abdul Aziz
(18:56) Naught prevented men from believing when the guidance came to them, or from asking pardon of their Lord, except the coming on them of the judgment of the people of olden days, or the coming of the doom before their own eyes.
(18:56) And We do not send the Noble Messengers except as Heralds of glad tidings and warnings
(18:56) We send the messengers only as deliverers of good news and warners. Those who disbelieve argue with false argument, in order to defeat the truth thereby. They take My Verses, and the warnings, for a joke.
Ahmed Raza Khan
(18:56) And We do not send the Noble Messengers except as Heralds of glad tidings and warnings; and the disbelievers debate by means of falsehood to drive away the Truth with it, and they took My signs and warnings they were given, as a mockery!
(18:56) We only send the messengers to bring good news and to give warning. Those who deny use fallacious arguments to nullify the truth, treating My revelations and My warnings as a jest.
(18:56) And We send not the Messengers except as bearers of good news and warners. But those who disbelieve, argue with falsehood, in order to refute the truth thereby. And they take My Ayat and that which they are warned for jest!
Ali Quli Qarai
(18:56) We do not send the apostles except as bearers of good news and as warners, but those who are faithless dispute fallaciously to refute thereby the truth, having taken My signs and what they are warned of in derision.
Hasan al-Fatih Qaribullah and Ahmad Darwish
(18:56) We send Our Messengers only to proclaim glad tidings and to give warning. But the unbelievers dispute with false arguments so that they may belie the truth. They have taken My verses and warnings in mockery.
That is translated surah Al kahf ayat 56 (QS 18: 56) in arabic and english text, may be useful.