There's probably no hard-and-fast rule, but I have two suggestions for abstracts, acknowledgements etc. in different languages.
One possibility is to typeset the respective text components basically as unnumbered chapters or sections (using the highest-ranking heading of your document). As a tweak, you could locally disable the \clearpage command so that multiple abstracts/acknowledegements will not automatically start a new page. (This is inconsistent compared to other chapters, but should make clear that these text components are variants [translations] of the same text.)
Another possibility (but only applicable for two or three languages and fairly short texts) is to typeset the abstracts/acknowledgements inside a multicols environment, separating the different languages by \columnbreak.
In the following minimal example that shows both possibilities, I've used the KOMA-Script class scrreprt and the geometry package in order to fit three abstracts into one page.
\documentclass{scrreprt}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[latin,ngerman,english]{babel}
\usepackage[hscale=0.7,vscale=0.8]{geometry}
\usepackage{multicol}
\setlength{\columnsep}{1.5em}
\usepackage{blindtext}
\begin{document}
\begingroup
\let\clearpage\relax
\chapter*{\abstractname}
\blindtext
\selectlanguage{latin}
\chapter*{\abstractname}
\blindtext
\selectlanguage{ngerman}
\chapter*{\abstractname}
\blindtext
\endgroup
\begin{multicols}{3}[\chapter*{Abstracts in English/Latin/German}]
\blindtext
\columnbreak
\selectlanguage{latin}
\noindent\blindtext
\columnbreak
\selectlanguage{ngerman}
\noindent\blindtext
\end{multicols}
\end{document}
