At the moment, ChessTask supports the two languages "German" and "English". In the download area you can find two executables, one with English the other with German as the default language.
No matter which you use, you can always set ChessTask to a language by starting it with either
ChessTask -english
or
ChessTask -german.
All menu entries, messages and the descriptions for the Informator symbols are displayed accordingly then.
The selected language also affects the HTML and LaTeX export. For example, if your ChessTask file contains special german characters like "ä" you have to set the language to "German". Otherwise, these characters do not appear in the LaTeX output (see also For the experienced LaTeX user).