Reading the article they are not generated files, but files that are never touched by developers. Translators will work with those files. I expect that for translators they have a different sparse checkout that only fetches .xlf files for their target languages.
Also plain text files are usually generated. They are arrays of 1s and 0s. No one wants to write that by hand.
I think that this is not a sensible definition of a generated file. A more sensible definition is that a generated file is created automatically from some source, which is not user input (i.e. an other file). This means generated files do not need to be kept under git, as long as their source is checked in.
Translations files, even if they are not created with a plain text editor but with some other tool that handles the XML layer, are clearly not generated, as long as the translation is done by a human.
For the app I work at the moment we use https://lokalise.com/. We add translation strings to a SaaS app, and then the translation team translate them. I've written a build tool that downloads the translation JSON files from the API using the CLI, or as part of our CI process. Other teams have tools that download their language packs for different iOS and Android apps. The translations are versioned in Lokalise and we using a branching strategy to manage the work. Lokalise has an option to generate xlf files (and JSON, xliff, arb, etc).
This is a very typical workflow. Most people are not out there modifying xlf files by opening them in a text editor. For a start, translations usually aren't done by developers.
(Huge shoutout to Lokalise btw. I can highly recommend it. It makes building a multi-lingual app across different platforms so much easier.)
You opted to keep translation files out of version control; you could also keep images there, or source files. All this stuff is the (pretty direct) output of non-deterministic human intervention.
(BTW, how do you build an old version of your application? Is lokalise able to give you the appropriate translations for a specific git commit / app version?)
.docx files are archives of xml-files. No one wants to write that by hand.
Or, in more words: The format of the files is just the representation on disk - it’s not directly connected to how the files are generated or edited. XML files can be written by hand with suitable editor support.
