There are some weird non-standard symbols here...
Left and right arrow in the top/left corner. What does it mean? "Swap"? Swap what?
On the arrow keys in another layer, Up and Down produce Page Up and Page Down, but Right and Left produce Tab and Back-Tab respectively.

I'm not an expert in 'standard' symbols.
When you make a layout
http://www.keyboard-layout-editor.com, if you open :
Character Picker > Keyboard-Layout-Editor Icons, you get a nice list of standard-ish icons.
Some don't look that standard to me or you but they are the best I found in the list.
The Left/right arrow in the top left is one of the tab symbols, though there is another one the is better.
The things you thought were Tab and back-tab are respectively Line-End and Line-Start...
I agree this isn't always straight forward...
But sometimes I like to have no text, only symbols.
PS : In case its not clear there are four layers 0, 1, 2 and 3. The 0 layer is by default for instance '?' on the top left blue key.
The bottom left arrow shifts to layer 1 giving '(', the second arrow right shifts to layer 2 '[', and both together to layer 3 '{'.
For the 'e' key we get 'e', 'E', 'f', 'F'.
The green keyboard key is for commands (remapping Ctrl-Alt-Win and Fn standard actions - but not Alt + digits).
Ctrl-Alt-Del is remapped to Alt Gr-Enter
The warning triangle in the top right corner is for , because there is no way to have that on this keyboard, its