I am new to i3 and would like to inquire if anyone knows how to show the combined traffic in Mbit/s running through (in and out) all network interfaces (ETH or WLAN) in real-time in the status bar?
I would like to do it via the config file if possible.
You can use i3pystatus instead of plain i3status. It has a module for network and showing the metric, below is the relevant doc:
https://i3pystatus.readthedocs.io/en/latest/configuration.html#internet-connectivity
An example config with what you want is here: https://i3pystatus.readthedocs.io/en/latest/configuration.html
By changing format_up you can change which metric is shown.