aside of installing Java (if that is missing) lomanager does not use any
of our repo mirrors but will download the LO-packages from the LibreOffice servers. That means whatever local repo you use in Synaptic, it doesn't matter. The only thing that does matter is that you use the current version of lomanager which corresponds to the current version of LO.
Andy, your problem is that you can not fully download one package which others can download, i.e. I can. This is a problem of your Internet connection, or the LO-download server, or, or, I don't quite know. But I will upload a LO3.4.1 offline installation later today and then send you a PM once it is in my dropbox. Then you can download and install this offline installation, will be the EN-US version. Sadly I don't know what else I could do to help you out.