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

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

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.