I've found out using Burning Board now that it makes more sense to install both German and English languages during installation. Reason being there are a few Multilingualism features in the Admin CP, that if you don't have both languages installed they are obsolete features you cannot use (because they require more than one language be installed) to make use of them.
But if I install both German and English, but later decide I only want to offer English only. It means I have to remove (uninstall the German language) because there's no 'global disable switch' to simply disable that language from being used. But removing the language is not ideal because of those features becoming obsolete then and the fact once the German language is removed, then there's no easy way of reinstalling it again without doing a fresh clean board install. So wouldn't it be better to add a global switch so you can keep both languages installed still, but be able to disable one of them completely without having to remove it.
Because as things are now. I cannot disable German language on my board from being used - without having to uninstall it. But I'd far sooner keep it installed and just disabled from using (as I might use it in future).