Apart from English (UK) I am frequently using German - which is supported - and French & Italian which are not supported. In the Extension Manager I see French but the icon “Bundled with LO” is off. Spanish is also on but I do not use it a lot. Spanish does not show in the drop down menu “Language” (for Selection, Paragraph, All Text).
I know LO has never been famous for language support but after all these decades it is about time to invest some manpower in this “language extension” project - what do you think?