One almost always can deconstruct these compound nouns into several words in order to write less abstract style. This then could become (also taking into account some of the criticisms): “durch die Typen der Parameter gesteuerte Auswahl der auszuführenden Methoden einer Funktion während der Laufzeit” . This the also includes that methods in Julia belong to functions.
I am not sure about “Multimethoden” or multimethods - this is as catchy as “multiple dispatch” while IMHO also not being precise enough. Also, in many cases these explanations are addressed to people not very well familiar with computer science definitions or other languages.
So as it stands now, I would write in an introduction something like this:
“Ein wesentliches Merkmal von Julia ist die durch die Typen der übergebenen Parameter gesteuerte Auswahl der auszuführenden Methode einer Funktion während der Laufzeit, auch parametertypengesteuerte Methodenauswahl oder Multiple Dispatch genannt” .
And may be English texts also could have this combination of precise description and catchy name.