Extra typographic characters with 3rd level chooser key

[gvnbm2018]

Hello everyone. I'm new to Debian and to Linux as well. Previous distributions that I have used were Ubuntu and Kubuntu. Both allowed to set a key to choose 3rd level characters and enable "extra typographic characters" in keyboard settings. Now I've installed Debian (Jessie) with LXDE, and can't find a way to set up this behavior. I've looked for solutions on the internet, but other than setting

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XKBOPTIONS="lv3:ralt_switch"

in /etc/default/keyboard or

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setxkbmap -option lv3:ralt_switch

in the terminal nothing can be found.
Even these options don't let me enter extra typographic characters.
How can I achieve it?

[Segfault]

I use very lean setup, no GUI configuration tools of any kind, I use xmodmap to set up my keyboard. Traditionally xinit parses ~/.Xmodmap. Below is mine as a sample.

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~ $ cat .Xmodmap 
keycode 133 = Mode_switch
keycode  13 = 4 dollar 4 cent
keycode  24 = q Q otilde Otilde
keycode  26 = e E EuroSign cent
keycode  30 = u U udiaeresis Udiaeresis
keycode  32 = o O odiaeresis Odiaeresis
keycode  38 = a A adiaeresis Adiaeresis
keycode  39 = s S scaron Scaron
keycode  40 = d D degree
keycode  52 = z Z zcaron Zcaron
keycode  58 = m M Greek_mu