It makes me feel much less lonely just to hear back from you. Thanks! I do still need help. I'm afraid that if three people visit the site at once, the error will start happening to them.
DreamHost tech support (in a not very friendly message) told me I had exceeded the limit on server memory and that was why I got all those errors. Following that lead, I did things aiming to reduce the memory requirements. One of them takes out parts of my design that my client wants (a soft requirement), but at least I'm not hitting that memory limit any more.
I think I am using my hyper-user-friendly theme framework (Headway) in a less than efficient way (I'm new to it). My bilingual plugin is slow. but I don't think it uses too much memory because I have very little content in either language yet. I would like to have a better understanding of how my configuration is using memory.
Here is something I'd really like to get your opinion about: When I started to get the errors, I was using three windows: one running the site to view work as I did it, one running the WordPress Pages/Widgets/Menus/Plugins functions, and one the Headway visual design functions. The problem started immediately after I added about 7 new pages, gave each of them a slightly different layout, and added them all to the menu. Given that I was only working in one window at a time, would those simultaneous windows explain the errors? I haven't been able to reproduce the errors by starting up the three screens again.
Then things started working again when I took out sliders from every possible page, substituting only one image each, and removed many instances of a widget displaying a small image in the sidebar. Headway works by having one layout reference blocks in another layout, except where there is a difference. In my case, every page had its own layout, and in most, the only difference was showing different images outside the content area.
If only I understood what changes would make the most difference!
I appreciate the chance to pick your brain about my issue.