The po plugin needs to be updated to match the urlto sub API and
signature changes. Else a wiki with the po plugin enabled cannot be
refreshed / rebuilt because of (correct) Perl errors.

My po branch contains a fix.
--[[intrigeri]]

> The commit looks sane to me, for what it's worth. Joey, please
> consider merging? --[[smcv]]

>> Merged. --[[Joey]] 

Also, I fear the lack of any useful `$from` parameter might break some
l10n'd link niceness when using `po_link_to = current` but I have not
investigated this yet.
--[[intrigeri]]

> If `urlto` is called without a second parameter, it means we need
> a URL valid from either the CGI URL or any page in the wiki,
> (so we'd previously have set the third parameter true), but we
> don't *necessarily* need an absolute URL - so return what you'd
> have returned if asked for an absolute URL, but looking like
> `/bugs/` rather than `http://ikiwiki.info/bugs/` if possible.
>
> It looks as though `beautify_urlpath` under `po_link_to = current`,
> and 3-argument `urlto`, aren't tested by `t/po.t` - perhaps you
> could add some test cases there? To test 3-argument `urlto` you'd
> need to add `$config{baseurl} = "http://example.com"` or
> something. --[[smcv]]

>> I'm leaving this bug report open until this can be checked. --[[Joey]] 

>>> My `ready/urlto` branch improves the test coverage. The bugfix from
>>> that branch fixes most of `po` too, but leaves behind some perhaps
>>> less-than-ideal behaviour: links where the current language is unknown,
>>> with `po_link_to = current`, always go to the master language,
>>> whereas perhaps it'd be better to go to the negotiated language in
>>> this case? --[[smcv]]

>>>> Thanks for taking care, thanks for these improvements!
>>>>
>>>> OTOH I consider any of these behaviours (either the brand new one
>>>> = link to master language, or the alternative one = link to
>>>> negotiated) as a regression. Any of these is contrary to what
>>>> `po_link_to = current` is supposed to do according to the
>>>> documentation.
>>>>
>>>> Let's be less technical, let me display my practical usecase
>>>> (making this possible was one of the main reasons I initially
>>>> implemented `po_link_to = current`).
>>>>
>>>> Summary: the current state of things is an annoying regression
>>>> and it needs to be fixed.
>>>>
>>>> Context: I participate in building a Live system based on Debian
>>>> Live; the project's multilingual website
>>>> ([T(A)ILS](https://amnesia.boum.org/) is built using ikiwiki. A
>>>> static / offline copy is shipped on ISO images; this is the way
>>>> end-user documentation lands on the CDs. Note that no webserver
>>>> runs on the Live system to serve this wiki, so `po_link_to =
>>>> current` is compulsory. A user can choose her preferred language
>>>> at boot time. Depending on her decision, The desktop shortcut
>>>> that points to the embedded documentation (i.e. static wiki)
>>>> links to a different entry point depending on the chosen
>>>> language.
>>>>
>>>> The previous (documented) behaviour was deadly simple:  if I am
>>>> presented a page in English (master language) it means it does
>>>> not exist in my preferred language; the computer always displays
>>>> me the best available version according to my needs. The new
>>>> behaviour brings a troubling seemingly random factor into the
>>>> user navigation experience and IMHO is a mess from a web
>>>> ergonomics point of view (no content negotiation available,
>>>> remember): I sometimes am shown an English page although it is
>>>> fully translated in my language one click away, and on the
>>>> contrary I sometimes I am shown the optimal page. This, is, well,
>>>> interesting. This practically forces the non-English speaking
>>>> website visitor to check the otherlanguages list on every single
>>>> page to make sure *herself* there is nothing better available,
>>>> and sometimes click on her preferred language link to get a page
>>>> she actually can read.
>>>>
>>>> I unfortunately might not be able to dedicate the needed time to
>>>> help fix this in a timely manner, so I don't want to urge anyone.
>>>> Take care!  --[[intrigeri]]

>>>>> I can see why this is bad, but to the best of my knowledge it's
>>>>> not a regression: each of the calls to 1-argument `urlto` was
>>>>> previously a call to 3-argument `urlto`, which always produces
>>>>> a fully absolute URL, so in either case there isn't enough
>>>>> context to know the current language. Links that were previously
>>>>> 2-argument `urlto` still have a defined second argument;
>>>>> I've just edited `plugins/write` to clarify why the second
>>>>> argument should be provided whenever possible. --[[smcv]]