If you regularly post in multiple languages, you have to select them all in your user settings.

However, having multiple languages selected will always display the same language list in the same order, even if you don’t post in that language.

For example, I post mostly in french but sometimes in english as well. Well, the lemmy front-end always puts english at the start of the list so every time I post in french, I need to re-select it which is kind of annoying. This add-on does it for you!