This page in a nutshell: The English Wikipedia is unable to maintain the long-term integrity of non-English redirects. Non-English redirects should be avoided except where the term is explained at the target.
We use English
This is the English Wikipedia. Our editors and administrators speak English. There are users willing and able to provide translations, and websites able to perform rudimentary translations, but this is not enough. Human translators are a precious resource, and their time is both valuable and hard to obtain. Automated translators can have trouble with verb cases, word senses, and homographs. The reality is that the English Wikipedia is only equipped to manage English content. It is not a matter of arrogance or narrow-mindedness, it is a matter of practicality.
Redirects can get complicated
Redirects can shift over time. Sometimes they are retargeted by a well-intentioned editor. Sometimes their target is moved, merged or deleted and they are updated as a result. Sometimes new articles cause a term to become ambiguous and disambiguation is performed. These are the usual causes for redirect discussions where the best course of action is not immediately clear. It sometimes requires thorough investigation to ensure that aspect of a redirect has been considered.
Error detection relies on numbers
Wikipedia relies heavily on a form of crowdsourcing for error detection. It takes many eyeballs on recent changes, what links here pages, watchlists and user contributions to identify and correct erroneous edits and many still slip through until a reader happens upon them. At the English Wikipedia these eyeballs are predominantly English-reading, and this correction mechanism fails for non-English content.
Non-English redirects should be avoided
Based on the three previous points, the proliferation of non-English redirects would introduce problems that our community of English editors would be unable to detect. That means redirects that are guilty of WP:RFD#DELETE #2–5, and violations of our principle of least astonishment.
Exceptions are okay
When a good reason exists to have a non-English redirect, we should have that non-English redirect. When naming conventions prescribe inclusion of non-English synonyms, that is a very good reason to have a non-English redirect. Any non-English redirect which appears in the article itself does not contribute to the problems explained above, because it is subject to our verifiability and neutrality policies as article content, and because astonishment is not a concern.
Uncertainty defaults to deletion
The burden of evidence lies with the editor wishing to keep non-English redirects. Our ability to secure translation services is limited, but it is there when necessary. However, we cannot take appropriateness of foreign-language redirects for granted. It can be difficult to determine the most appropriate target for an obscure but useful search term, or to recognize when a misspelled word is in fact a plausible misspelling for multiple unrelated concepts, even when we are fluent in the language. Just as a non-English speaker may not realize that a misspelling of 'shot'could be offensive, you may not realize the issues surrounding a non-English misspelling if you are not fluent in that language. Redirects can get complicated, and complications often require fluency to recognize.