In Microsoft Windows, the Hebrew keyboard layout has Hebrew characters in the basic state, English capital letters in Shift state or in Caps Lock state, but if you use Shift when Num Lock is on, you can enter Hebrew Niqqud - diacritical/pronunciation signs: Shift-Num-row-8 is Qamats, Shift-Backslash is Qubuts and so on.
Now, whether you think that's a good layout or not - I'm used to it. And I want it on Linux. In the olden days of XFree86 X11R6 I remember there was a way to mess the xkb to get a Hebrew layout variant that had something similar: SI 1452. But I don't see it mentioned in my Keyboard Layout dialog (XFCE on GNU/Linux Mint 18.2, based on Ubuntu 16.04). And Googling, I seem to only find highly outdated instructions.
What should I do?