Linking to redirects
It has been the default policy, as implemented in
interwiki.py, not to add links to the same form on another wikt when the target of the link is a redirect.
It is not clear whether this was ever intentional, or a side-effect of the hacking of the wikipedia interwiki code to operate in "wiktionary mode". (One person has defended it as intentional and correct, but has not offered any argument besides that it is somehow vaguely wrong to link to redirects.)
It would be much more useful to have a standard policy of always linking to redirects in the other wikt.
Note: At this time, Interwicket only adds links to redirects when it is configured to for specific wikts; the others are treated as default: it neither adds links to redirects nor removes them if found.
Wikts often use different canonical forms for a given idiom, either in a standard way or arbitrarily.
For example: en:fix und fertig and de:fix und fertig sein are the entries. On the en.wikt, en:fix und fertig sein is a redirect to the entry, on de.wikt, en:fix und fertig is a redirect. This works well with iwiki links to redirects, but is broken without: en.wikt links to redirects, de.wikt does not (table as of status 31 January 2009)
|user starts at||sees page||iwiki link||arrives at|
|en:fix und fertig||en:fix und fertig||de:fix und fertig||de:fix und fertig sein|
|en:fix und fertig sein||en:fix und fertig||de:fix und fertig||de:fix und fertig sein|
|de:fix und fertig sein||de:fix und fertig sein||(none)||(can't get there)|
|de:fix und fertig||de:fix und fertig sein||(none)||(can't get there)|
If de.wikt allowed links to redirects, this would work exactly as it should. And if either wikt (or any other language also linking these titles) moves from one to the other (reverses redirect) it continues to work correctly without modifying the interwiki links.
Different wikts use various standard typography; the en.wikt uses a straight apostrophe in (almost) all cases, while the fr.wikt uses ’ ("right single quotation mark") in the same cases. So en:z' is the standard form on en, and fr:z’ on the fr.wikt. Linking to the redirects, en:z’ and fr:z' provides the reader with access to the standard form on the other wikt. (Note that as of this writing, a user has added a non-standard iwiki to the fr.wikt page ;-).
The issue here is linking to the redirects in both directions so the entries can be found. (And not to try to impose the standard apostrophe used on the other wikts.)
The English wikt has entries for 食 (U+98DF) and a modified form of the radical 飠 (U+98E0), (radical 184), the zh wiktionary combines the entries, with the form redirected to the radical. Likewise the simplified form 饣 is redirected to the traditional form. The interwiki links from en.wikt all work correctly, as it links to these redirects; other wikts that are not linking to redirects have no interwiki links for these characters to the zh.wikt, a rather large omission.
For example, while the en.wikt has entries for cerveza and cervezas, the ca.wikt (Catalan) redirects ca:cervezas to ca:cerveza. A reader starting on the Catalan wiktionary will always see ca:cerveza, and iwiki to the singular form in the en.wikt (which of course has the inflections linked in the text). A reader starting with the en.wikt will see the form looked for; following the iwiki link for ca will arrive at ca:cerveza in either case.
The Bulgarian wiktionary also has a very large number of bot-generated redirects to (presumably) a base form.
Vowel markings (Arabic, Hebrew, etc)
Different wikts have very different policies (or non-policies) concerning redirects from forms to the "defective" form, without markings. (Or to different markings.) Linking to the redirects is a best effort case for getting the reader to the desired entries.
There still are a number of redirects left over from the "conversion script", although we've deleted most from en.wikt; most wikts had few or no entries when the script was run. In any case, it is not harmful to end up at a different capitalization on the other wikt; it may be the desired form; the redirect may be intentional.
A number of other cases exist due to local policies and conventions. For example ur:business redirects to the Urdu word, rather than being an entry for the English word with the Urdu definition. (It isn't clear whether this is policy, convention, or mistake ...) So en:business has a link to the intended (?) entry in the Urdu wiktionary.
Move leftovers, junk
Move leftovers from errors might be useful, but probably not; but will only be linked to from an actual entry, so they are words in some language. Pure junk (vandalism, etc) will exist whether redirects or not, but if not words, there won't be any valid entries to link to them anyway.
Linking to redirects in the other wikt is an all-around win, the negatives are almost non-existent. We really should make the default policy be linking to redirects; while still permitting wikts to have specific policy (of course). However, it might be reasonable with the appropriate community discussion to make linking to redirects universal policy.