In IGV the shortcut for zooming in on a graph is Ctrl + "=". This shortcut is common because "=" is on the same key as "+" on the US keyboard and can be used without pressing the Shift-Key. On other keyboards "=" and "+" are not on the same key and both not even on the first level (without shift) of the keyboard. Therefore Ctrl + "=" does often not work on non-US keyboards (e.g. German/Swiss layout). There is no easy way to implement this manually for all keyboard-layouts to work. Best to use an available library/function that supports different keyboard layouts.