Visualize Installation Variables in own Toolbar


I want to make my own URcaps toolbar which visualises installation variables.

Unfortunately I have difficulties to get the variable value of any type of variable, also “installation variables”.
I know it is the same question as stated in Get Variable values in Toolbar - #2 by a.mora, but I don’t know how "installation variables might be mapped with read_output_integer_register(21) variables.

Thx for any comment.