Change keyboard layout with a keystroke + show it in the status bar.

Download i3-keyboard-layout, make sure it's executable (chmod + x <file>), and store it somewhere in your home directory (or in your $PATH if you prefer)

Assign a keystroke in your i3 configuration to switch to different layouts:

# ~/.config/i3/config

bindsym $mod+z exec path/to/i3-keyboard-layout set us
bindsym $mod+x exec path/to/i3-keyboard-layout set es
bindsym $mod+x exec path/to/i3-keyboard-layout set de:neo

Alternatively (or aditionally), you can use a single keystroke to cycle through a list of your most used layouts:

# ~/.config/i3/config

bindsym $mod+space exec path/to/i3-keyboard-layout cycle us es de:neo

Each time you press that key, the next layout on the list will be selected.

If you want to use layouts with variants, you can use quotes, like this:

# ~/.config/i3/config

bindsym $mod+space exec path/to/i3-keyboard-layout cycle us "us euro"

NOTE: You can skip this part if you use some kind of tray indicator such as sbxkb, which is probably what you want if you prefer a flag instead of the name of the layout.

A subcommand is included to display the current layout on the i3status bar. On your bar configuration, you need to pipe i3status onto the i3status subcommand:

# ~/.config/i3/config

bar {
  # status_command i3status # this is the usual default configuration
  status_command i3status | i3-keyboard-layout i3status
}

i3status needs to be configured tou output the i3bar JSON format (which is usually the default):

# ~/.config/i3status/config

general {
  output_format = i3bar
}

At this point only prepending the layout at the left of everything else is supported.