Andrew,

As test I added this customiso.lin file:

;;
;;  Custom QCAD linetypes for metric system
;;
*DASHEDC,Custom Dashed _ _ _ _ _ _ _ _ _ _ _ _ _ _
A, 2, -1 
*DOTTEDC,Custom Dotted . . . . . . . . . . . . . .
A, 0, -1  

All fine but they are listed as 'DASHEDC' and 'DOTTEDC'.

Kinda expected that the description would be used to list them.
All seemingly according the standard types.

Where for example

*DASHED2,Dashed (.5x) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
A, 6.35, -3.175

is listed as 'Dashed (.5x)' and not as 'DASHED2'

Most probably because 'types' are translated and mine are not in that standard list.
It would still be appropriate to use the descriptor.
Then I have the option to include that in English or in an even custom language.

Regards,
CVH