XRDP add layout - xfce

Question

On Debian 8 installed XRDP + xfce4. There is no possibility to add a new layout to system - the "Add" button is disabled: after logging in go to the "Application Menu - Settings - Keyboard" select "Layout" and see the following picture: see screenshot.
In the directory /etc/xrdp/ there are files:
km-0407.ini
km-0409.ini
km-040c.ini
km-0410.ini
km-0419.ini
km-041d.ini
rsakeys.ini
sesman.ini
startwm.sh
xrdp.ini
km-0419.ini - layout, which I need.
How to add a keyboard layout?
I tried to run inside a terminal session (under root) commands:
setxkbmap
and
xrdp-genkeymap /etc/xrdp/km-0419.ini
In response to the first command I get:
XKB extention not present on: 10.0
second silently executed, nothing happens.
The same commands is a terminal session (on a host-machine) reported:
Can not open display «default display»
and
unable to open display ""

Answer 1

I had a trouble with Debian 9 + xfce + xrdp.
The trouble was the additional layouts disappeared when I reconnected by RDP.
I'm not sure this is exactly you are looking for, I apologize if it is not.
Maybe my experience will help you to figure out how to resolve your trouble.
Also I do not know if it works for your version of xrdp.
For example here is solution for Russian keyboard.
It returns all keyboard layouts settings to default when you start new RDP session.
So there are two ways to resolve it.
Run the command to change your settings to preferable after any RDP login.
setxkbmap -layout us,ru -variant ',winkeys' -option 'grp:alt_shift_toggle,grp_led:scroll'
Or change xrdp config to make it use the settings you want.
What helped me is correcting file /etc/xrdp/xrdp_keyboard.ini
(pay attention for sections [rdp_keyboard_ru] and [layouts_map_ru])
You can use it for another's languages by analogy.
Here is an example of /etc/xrdp/xrdp_keyboard.ini file of mine.
You can see at the end of the file I use my custom sets:
;
; RDP Keyboard <-> X11 Keyboard layout map
;
; How this file works:
; 1. load the file and scan each section to find matching "keyboard_type"
; and "keyboard_subtype" based on the values received from the client.
; If not found, then jump to default section.
; 2. in the selected section, look for "rdp_layouts" and "layouts_map".
; Based on the "keylayout" value from the client, find the right x11
; layout value.
; 3. model/variant are inferred based on the "keyboard_type" and
; "keyboard_subtype", but they can be overridden.
;
;
; RDP Keyboard Type (http://msdn.microsoft.com/en-us/library/cc240563.aspx)
;
; 0 is not a valid value
;
; 1 - IBM PC/XT or compatible (83-key) keyboard
; 2 - Olivetti "ICO" (102-key) keyboard
; 3 - IBM PC/AT (84-key) or similar keyboard
; 4 - IBM enhanced (101- or 102-key) keyboard
; 5 - Nokia 1050 and similar keyboards
; 6 - Nokia 9140 and similar keyboards
; 7 - Japanese keyboard
;
; RDP Keyboard Subtype is vendor dependent. XRDP defines as follows:
;
; 0 is not a valid value
;
; 1 - Standard
; 2 - FreeRDP JP keyboard
; 3 - Macintosh
; ... - < any vendor dependent subtype >
;
; The list can be augmented.
;
; default
[default]
; keyboard_type and keyboard_subtype is not read for default section. It
; is only a placeholder to keep consistency. Default model/variant are
; platform dependent, and could be overridden if needed.
keyboard_type=0
keyboard_subtype=0
; user could override variant and model, but generally they should be inferred
; automatically based on keyboard type and subtype
;variant=
;model=
; A list of supported RDP keyboard layouts
rdp_layouts=default_rdp_layouts
; The map from RDP keyboard layout to X11 keyboard layout
layouts_map=default_layouts_map
[default_rdp_layouts]
rdp_layout_us=0x00000409
rdp_layout_de=0x00000407
rdp_layout_fr=0x0000040C
rdp_layout_it=0x00000410
rdp_layout_jp=0x00000411
rdp_layout_jp=0xe0010411
rdp_layout_jp=0xe0200411
rdp_layout_jp=0xe0210411
rdp_layout_kr=0x00000412
rdp_layout_ru=0x00000419
rdp_layout_se=0x0000041D
rdp_layout_ch=0x00000807
rdp_layout_pt=0x00000816
rdp_layout_br=0x00000416
rdp_layout_pl=0x00000415
; <rdp layout name> = <X11 keyboard layout value>
[default_layouts_map]
rdp_layout_us=us
rdp_layout_de=de
rdp_layout_fr=fr
rdp_layout_it=it
rdp_layout_jp=jp
rdp_layout_kr=kr
rdp_layout_ru=ru
rdp_layout_se=se
rdp_layout_ch=ch
rdp_layout_pt=pt
rdp_layout_br=br(abnt2)
rdp_layout_pl=pl
; if two sections have the same keyboard_type and keyboard_subtype, then
; the latter could override the former.
[rdp_keyboard_mac]
keyboard_type=4
keyboard_subtype=3
rdp_layouts=default_rdp_layouts
layouts_map=rdp_layouts_map_mac
[rdp_keyboard_jp]
keyboard_type=7
keyboard_subtype=2
model=pc105
rdp_layouts=default_rdp_layouts
layouts_map=default_layouts_map
[rdp_layouts_map_mac]
rdp_layout_us=us
rdp_layout_de=de
rdp_layout_fr=fr
rdp_layout_jp=jp
rdp_layout_kr=kr
rdp_layout_it=it
rdp_layout_ru=ru
rdp_layout_se=se
rdp_layout_ch=ch
rdp_layout_pt=pt
rdp_layout_br=br(abnt2)
rdp_layout_pl=pl
[rdp_keyboard_ru]
keyboard_type=4
keyboard_type=7
keyboard_subtype=1
model=pc105
options=grp:lctrl_lshift_toggle,compose:ralt
variant=,
rdp_layouts=default_rdp_layouts
layouts_map=layouts_map_ru
[layouts_map_ru]
rdp_layout_us=us,ru
rdp_layout_ru=us,ru

Answer 2

look at $HOME/.config/xfce4/xfconf/xfce-perchannel-xml/keyboard-layout.xml
setxkbmap -layout us,ru -variant ',' -option 'grp:win_space_toggle'