Allow setting a default language

### Describe the problem that you'd like solved
The Open Library catalogs books in every language they've ever been published in, which is fantastic, but currently that also means that when I open, say, the books in the Harry Potter series, half of them are in a different language.

### Proposal & Constraints
It would be great if users could set a default language (or country), and be treated with the localized (or non-localized) version of that book to where they are.

Whether this is set by country or by language, there might have to be a fallback for books that aren't published in that country / language. This could probably just be the first published version.

### Additional context

### Stakeholders

No files, tests, or entry points are named. Start by locating how book-series editions are selected and where user language or country preferences are handled. Done means users can set a default language or country, localized editions are preferred with a defined fallback, and the behavior is covered by relevant tests.

Written by the indexing model from the issue text.