- go to the wikisource page of a certain language, for example English https://en.wikisource.org
- search for the exact title of something in a different language. For example: "Les Enfants du capitaine Grant" https://en.wikisource.org/w/index.php?search=Les+Enfants+du+capitaine+Grant
- See some results. You have to click the author's page, find the book in the list again and click on it.
This is a poor example because the word "Grant" appears in the text of the page for both English and French, so the book in English is the second result but I think you get my point. It should just send me to the English translation (or whichever language Wikisource I'm on) directly since I typed the exact match of a book title that appears on a different language Wikisource.
This could work by automatically creating redirects when articles are created or moved, or by changing the code of the search page.
It should also be like on Wikipedia where it'll show you "We found the following results from French Wikisource"