Latin sentence for you to paraphrase

The following is taken from an entry on Wotton, Sir Henry, page 279 of A Dictionary of Diplomacy 2nd edition. G. R. Berridge and Alan James

Please help me paraphrase the meaning of bolded part.

It was intended, of course, as a pun on the word 'lie', which in this context could mean either 'sojourn abroad' or 'tell lies abroad'. (It is not known whether Wotton also meant it to refer to having sexual relations.) Unfortunately for Sir Henry, while he appears to have conceived the saying in English, he wrote it out in Latin: "Legatus est vir bonus pergre missus ad mentiendum Reipublicae causa." Acoording to his friend Isaak Walton, 'the word lie (being the hinge upon which the conceit was to turn ) was not so expressed in Latin [mentiendum], as would admit (in the hands of an enemey especially ) so fair a construction as Sir Henry thought in English'.