The first (and only) translation of this novel into English was published in 1786, and the translator was Thomas Holcroft. The title page reads London: Printed for G. G. J. and J. Robinson ... 1786. Montolieu's work was widely read in this translation. I here quote from two contemporary reviews and a comment in a private letter:
From Critical Review:
A Romance which differs, in its progress and its events, from the volumes which crowd and disgrace a circulating library, forms a new era in literature. To interest, and attract, it is necessary to avoide the usual trait of incident; to diversify the faces to whch we have been so much accustomed to survey; at the same time, to avoid what is only uncommon, if destitute of probability or the resemblance of nature; to neglect absurd refinements, and superficial reflections.
The author of Caroline has started from vulgar bounds, and her narrative is natural, interesting and in some degree new."
From The Monthly Review [Samuel Badcock]:
In this beautiful and interesting novel, the lights and shades of character are blended with great ingenuity: and in every part of it we discover the hand of an elegant and skilful artist. With wonderful energy and address, the Authoress unfolds the secret springs and complex movements of the human heart; and so forcibly are the different feelings that agitate the soul, delineated by her magic pencil, that they strongly awaken the sympathy of the reader, and interest him in the distress of the story.
Finally, of Holcroft's translation, Mary Russell Mitford remarked that
'if ever one happpens to take up an English version of a French or a German book of the period [1785-1810] and if that version have in it the zest and savour of original writing, we shall be sure to find the name [or not, for many of his translations are anonymous] of Thomas Holcroft on the title-page'. Here is the heroine's reaction to her bridegroom: 'Instantly hiding her eyes with her hands, [Caroline] gave a piercing shriek and disappeared like a flash of lightning at midnight ... The Count of Walstein was, in fact, little more than thirty; but an enormous scar on one cheek, a countenance excessively meagre and of a livid yellow, round shoulders, and, instead of hair, a perriwig ... His large black eye was fine; but, alas! it was single ...' Colby, Holcroft, p. 54; Black 617.
Holcroft worked as a translator to supplement his income, but his choice of book reflect his liberal outlook (I use the adjective in the modern sense); another of his translations (which connects his work to Montolieu's work was of Stéphanie-Félicité de Genlis's Les Veillées du Château as Tales of the Castle: Or, Stories of Instruction and Delight (1785). Genlis was Montolieu's friend and the mood and conscious aims of her book recall those of Montolieu; Jane Austen read and admired both books.
See The English Novel, 1770-1729: A Bibliographical Survey of Prose Fiction Published in the British Isles, edd. James Raven, Antonia Forster, and Stephen Bending (Oxford: At the University Press, 2000), 1786:34, pp. 385-86.