I had assumed the author didn't limit his statements to web browsers. If it's an application on a user's box, they should be using the language the OS provides.

In the case of less complex hardware, IoT or embedded devices with localization support, you would likely have another strategy if it doesn't have a setup process. For something without internet or GPS, you can't do this obviously. For something without a GUI, it's unlikely to have localization support without direct design consideration for it's destination.