I'm trying to install German as a second language in Ubuntu 18.04, but every time I do, I get a 'Failed to fetch HTTP' error. I'm definitely on the internet, as I've tried surfing the web in Firefox. The method I've been using to install the new language is to open Settings > Language and Region, click Manage Installed Languages, then Install/Remove Languages. I presume this is correct? It certainly seems to be. If anyone can shed any light on this, I'd be grateful. I have limited experience with Linux, but am experienced in the Mac.