In the recent blog post on how to make a web part works with different section backgrounds using CSS variables, I already covered. At the same time, this works perfectly for just regular web parts. There are specific scenarios, where this approach fails.
SharePoint Online for a long time, has multilingual support. On classic experience, there were language packs and Variations available for that. Yet also the modern experience has multilingual capabilities for that.
It might look that SharePoint is well capable of providing the language chosen by the user for the user. While I had to take a closer look under the hood over the last couple of month, multilingual and SharePoint has a complicated relationship.