In English, I've only found this very limited translation by Yourgrau and Mandelstam.
From these facts we may even now draw the conclusion that the
domain of validity of the principle of least action has reached far beyond the
boundaries of the mechanics of ponderable bodies. Maupertuis’ high hopes for
the absolute general validity of his principle appear to be approaching their
fulfilment, however slender the mechanical proofs and however contradictory the
metaphysical speculations which the author himself could at the time adduce in
support of his new principle. Even at this stage, it can be considered as highly
probable that it is the universal law pertaining to all processes in nature. . . . In
any case, the general validity of the principle of least action seems to me
assured, since it may claim a higher place as a heuristic and guiding principle in
our endeavour to formulate the laws governing new classes of phenomena.
Perhaps useful for other readers is the full Russian translation in Полак, Л.С. (ред.), Вариационные принципы механики: Сборник статей классиков науки, 1959. There's a djvu file here. The file can be converted to pdf at, e.g., http://www.djvu-pdf.com/. The Russian-translated paper is at page 430ff (pdf-page 434ff).