Sorting by language has come up before. Catch is that if the language is english most uploaders don't bother to mention it in the title. If it ain't in the title then there is usually no practical of eliminating even the bulk of the wrong languages.
So, when practical why not add a language tag by default?
As example "my scrapbook by AN Other.epub" could be auto-renamed "(eng) my scrapbook by AN Other.epub"
There are obvious limitations. Compressed files lock if the name is changed so, unless they can be altered not to lock they can't be renamed. However, it should be an easy fix for those that can and every little bit helps.
It might even get popular as a naming convention for compressed files.
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