I form abstract.tex as

\renewcommand{\abstractname}{Abstract}
\begin{abstract}
... % eng version
\end{abstract}

\renewcommand{\abstractname}{Kurzfassung}
\begin{abstract}
... % de version
\end{abstract}



How to add Abstract and Kurzfassung ( both) in the table of the contents?

• Welcome to TeX SX! What are you missing? – Bernard Aug 1 '20 at 12:44
• @Bernard I need to add content in the table of content. – Noel Miller Aug 1 '20 at 12:47
• Oh! When you' reading the table of contents, you need to know where it is? :-) – Bernard Aug 1 '20 at 13:51

\renewcommand{\abstractname}{...}

As you have not provided an MWE I guessed that you might want the abstracts' ToC entries to be like a chapter. If they are more like a section then change the chapter to section. There is more information in the tocloft package manual but I don't think that you need the package for what you want.