Posts Tagged ‘plural’ summer update

Monday, July 7th, 2014

It’s been a busy while since last update, but how could I have not worked on ;) Here is an update on my current activities.
In this episode:

  • we provide translations for over 70 % of users of the new Wikipedia app,
  • I read a book on networking performance and get needy for speed,
  • ElasticSearch tries to eat all of us and our memory,
  • HHVM finds the place not fancy enough,
  • Finns and Swedes start cooperating.


Naturally, I have been thinking of ways to further improve performance. I have been running HHVM as a beta feature at many months now, but I have kept turning it on and off due to stability issues. It is currently disabled, but my plan is to try the Wikimedia packaged version of HHVM. Those packages only work in Ubuntu 2014.04, so Siebrand and I first have to upgrade the server from Ubuntu 2012.04, as we plan to later this month (July). (Update: done as of 2014-07-09, 14 UTC.)

Map of some translators

A global network of translators is not served well enough from a single location

After reading a book about networking performance I finally decided to give a content distribution network (CDN) a try. Not because they can optimize and cache things on the fly [1], nor because the can do spam protection [2], but because CDN can reduce latency, which is usually the main bottleneck of web browsing. We only have single server in Germany, but our users are international. I am close to the server, so I have much better experience than many of our users. I do not have any numbers yet, but I will do some experiments and gather some numbers to see whether CDN helps us.

[1] MediaWiki is already very aggressive in terms of optimizations for resource delivery.
[2] Restricting account creation already eliminated spam on our wiki.

Wikimedia Mobile Apps

Amir and I have been closely working with the Wikimedia Mobile Apps team to ensure that their apps are well supported. In just a couple weeks, the new app was translated in dozens languages and released, with over 7 millions new installations by non-English users (74 % of the total).

In more detail, we finally addressed a longstanding issue in the Android app which prevented translation of strings containing links. I gave Yuvi access to synchronize translations, ensuring that translators have as much time as possible to translate and the apps have the latest updates before being released. We also discussed about how to notify translators before releases to get more translations in time, and about improvements to their i18n frameworks to bring their flexibility more in line with MediaWiki (including plural support).

To put it bluntly, for some reason the mobile i18n frameworks are ugly and hard to work with. Just as an example, Android did not support many languages at all just for one character too much; support is still partial. I can’t avoid comparing this to the extra effort which has been needed to support old versions of Internet Explorer: we would rather be doing other cool things, but the environment is not going to change anytime soon.


I installed and enabled CirrusSearch on for the first time, we have a real search engine for all our pages! I had multiple issues, including running a bit tight on memory while indexing all content.

Translate’s translation memory support for ElasticSearch has been almost ready for a while now. It may take a couple months before we’re ready to migrate from Solr (first on, then Wikimedia sites). I am looking forward to it: as a system administrator, I do not want to run both Solr and ElasticSearch.

I want to say big thanks to Nik for helping both with the translation memory ElasticSearch backend and my CirrusSearch problems.

Wikimedia Sweden launches a new project

I am expecting to see an increased activity and new features at thanks to a new project by Wikimedia Sweden together with InternetFonden.Se. The project has been announced on the Wikimedia blog, but in short they want to bring more Swedish translators, new projects for translation and possibly open badges to increase translator engagement. They are already looking for feedback, please do share your thoughts.

MediaWiki i18n explained: {{PLURAL}}

Sunday, January 5th, 2014

This post explains how MediaWiki handles plural rules to developers who need to work with it. In other words, how a string like “This wiki {{PLURAL:$1|0=does not have any pages|has one page|has $1 pages}}” becomes “This wiki has 425 pages”.


As mentioned before we have adopted a data-based approach. Our plural rules come from Unicode CLDR (Common Locale Data repository) in XML format and are stored in languages/data/plurals.xml. These rules are supplemented by local overrides in languages/data/plurals-mediawiki.xml for languages not supported by CLDR or where we are yet to unify our existing local rules to match CLDR rules.

As a short recap, translators handle plurals by writing all possible different forms explicitly. That means that there are different forms for singular, dual, plural, etc., depending on what grammatical numbers the language has. There might be more forms because of other grammatical reasons, for example in Russian the grammatical case of the noun varies depending on the number. The rules from CLDR put all numbers into different boxes, each box corresponding to one form provided by the translator.


The plural rules are stored in localisation cache (not to be confused with message cache and many other caches in MediaWiki) with other language specific localisation data. The localisation cache can be stored in different places depending on configuration. The default is to use the SQL database, but they can also be in CDB files as they are at the Wikimedia Foundation and

The whole process starts 1) when the user runs php maintenance/rebuildLocalisationCache.php, or 2) during a web request, if the cache is stale and automatic cache rebuild is allowed (as by default).

The code proceeds as follows:


  • LocalisationCache::getPluralRules fills pluralRules
    • LocalisationCache::loadPluralFiles loads both xml files, merges them and stores the result in in-process cache
  • LocalisationCache::getComplisedPluralRules fills compiledPluralRules
    • LocalisationCache::loadPluralFiles returns rules from in-process cache
    • CLDRPluralRuleEvaluator::compile compiles the standard notation into RPN notation
  • LocalisationCache::getPluralTypes fills pluralRuleTypes

So now for the given language we have three lists (see table 1). The pluralRules are used in frontend (JavaScript) and the compiledPluralRules are used in the backend (PHP) with a custom evaluator. Tim Starling wrote the custom evaluator for performance reasons. The pluralRuleTypes stores the map between numerical indexes and CLDR keywords, which are not used in MediaWiki plural syntax. Please note that Russian has four plural forms: the fourth form, called other, is used when none of the other rules match and is not stored anywhere.

Table 1: Stored plural data for Russian
pluralRuleTypes pluralRules compiledPluralRules
“one” “n mod 10 is 1 and n mod 100 is not 11” “n 10 mod 1 is n 100 mod 11 is-not and”
“few” “n mod 10 in 2..4 and n mod 100 not in 12..14” “n 10 mod 2 4 .. in n 100 mod 12 14 .. not-in and”
“many” “n mod 10 is 0 or n mod 10 in 5..9 or n mod 100 in 11..14” “n 10 mod 0 is n 10 mod 5 9 .. in or n 100 mod 11 14 .. in or”

The cache also stores the magic word PLURAL, defined in languages/messages/MessageEn.php and translated to other languages, so in Finnish language wikis they can use {{MONIKKO:$1|$1 talo|$1 taloa}} if they so want. For compatibility reasons, in all interface translations these magic words are used in English.

Invocation on backend

There are roughly three ways to trigger plural parsing:

  1. using the plural syntax in a wiki page,
  2. calling the plural parser with Message object with output format text,
  3. using the plural syntax in a message with output format parse, which calls full wikitext parser as in 1.

In all cases, we will get into Parser::replaceVariables, which expands all magic words and templates (anything enclosed in double braces; sometimes also called {{ constructs). It will load the possible translated magic words and see if the {{thing}} in the wikitext or message matches a known magic word. If not, the {{thing}} is considered a template call. If the plural magic word matches, the parser will call CoreParserFunctions::plural which will take the arguments, make them into an array, call the correct language object with Language::convertPlural( number, forms ): see table 2 for function call trace.

In the Language class we first handle explicit plural forms explained in a previous post on explicit zero and one form. If any explicit plural form doesn’t match, they are removed and we will continue on with the other forms, calling Language::getPluralRuleIndexNumber( number ), which first loads the compiled plural rules into the in-process cache, then calls CLDRPluralRuleEvaluator::evaluateCompiled which returns the box the number belongs to. Finally we take the matching form given by the translator, or the last form provided. Then the return value is substituted in place of the plural magic word call.

Table 2: Function call list for plural magic word
Message::parse Message::text
  • Message::toString
  • Message::parseText
  • MessageCache::parse
  • Parser::parse
  • Parser::internalParse
  • Message::toString
  • Message::transformText
  • MessageCache::transform
  • Parser::transformMsg
  • Parser::preprocess
  • [The above lists converge here]
  • Parser::replaceVariables
  • PPFrame_DOM::expand
  • Parser::braceSubstitution
  • Parser::callParserFunction
  • call_user_func_array
  • CoreParserFunctions::plural
  • Language::convertPlural
  • [Plural rule evaluation]

Invocation on frontend

The resource loader module (implemented in class ResourceLoaderLanguageDataModule) is responsible for loading the plural rules from localisation cache and delivering them together with other language data to JavaScript.

The resource loader module mediawiki.jqueryMsg provides yet another limited wikitext parser which can handle plural, links and few other things. The module mediawiki (global mediaWiki, usually aliased to mw) provides the messaging interface with functions like mw.msg() or mw.message().text(). Those will not handle plural without the aforementioned mediawiki.jqueryMsg module. Translated magic words are not supported at the frontend.

If a plural magic word is found, then it will call the frontend convertPlural method. These are provided in few hops by the module mediawiki.language which depends on and mediawiki.cldr. The latter depends on mediawiki.libs.pluralruleparser, which evaluates the (non-compiled) CLDR plural rules to reach the same result as in the PHP side and is hosted at GitHub, written by Santhosh Thottingal of the Wikimedia Language Engineering team.

Review of Gettext po(t) file format

Wednesday, November 20th, 2013

Gettext shows its age both in developer and translator friendliness. What’s wrong with the old known localisation file formats which Google and Mozilla among others are so keen to replace? I don’t have a full answer to that. Gettext is clearly quite inflexible compared to Mozilla’s file format (which is almost a programming language) and it does not support many of the new features in Google’s resource bundles.

My general recommendation is: use the file format best supported by your i18n framework. If you can choose, prefer key based formats. Only try new file formats if you need the new features, because tool support for them is not as good. There is also no clarity which of the new file formats will “win” the fight and become popular.

When making something new, it is good to look back. The motivation why I wrote this post initially was my annoyances writing a tool which supports this format, but the context I’m going to give is completely different. It has been waiting as draft to be published for a long time because it lacked context where it makes sense. Maybe this also helps people, who are wondering what localisation file format they should use.

Enough of the general thoughts. But let’s start this evaluation with the good things:
Can support plural for many languages. The plural syntax is flexible enough to cover at least most if not all of world’s languages.
Fuzzy translations. It has a standard way to mark outdated translations, which is a necessity for this format which does not identify strings.
Tool support. Gettext can be used in many programming languages and there are plenty of tools for translators.

And then the things I don’t like:
Strings have no identifiers. This is my biggest annoyance with Gettext. Strings are identified by their contents, which means that fixing a typo in the source invalidates all translations. It also makes it impossible to keep any track of history. This causes another problem: Identical strings are collapsed by default. This is especially annoying since in English words like Open (action) and Open (state) are the same but in other languages they are different. This effectively prevents proper translations, unless a message context is provided, but here lies another problem: Not all implementations support passing context. Last time I checked this was the case at least in Python.
And one nasty corner case for tool makers is that empty context is different from no context. If you don’t handle this right you will be producing invalid Gettext files.
I listed plural support above as a plus, but it is not without its problems. One string can only have plural forms depending on one variable. This forces the developers to use lego sentences when there is more than one number, or force the translators to make ungrammatical translations. Not to mention that, in Arabic and other languages where there can be five or even more forms, you need to repeat the whole string as many times with small changes. Lots of overhead updating and proofreading that, as opposed to an inline syntax where you only mark the differences. To be fair, with an inline syntax it might hard to see how each plural form looks in full, but there are solutions to that.
There is no standard way to present authorship information except for last translator. The file header is essentially free form text, making it hard to process and update that information programmatically. To be fair, this is the case for almost all i18n file formats I’ve seen.
The comments for individual strings are funky. There are different kinds of comments that start with “#,” “#|”, not documented anywhere as far as I know, and the order of different kinds of comments matters! Do it wrong and you’ll have a file that some tools refuse to use. Not to mention that developers can also leave comments for the translators, in addition to the context parameter (so there are two ways!): the translators might or might not see them depending on the tool they use and on what is propagated from the pot file to the po file. It is quite a hassle to keep these comments in sync and repeated in all the translation files.

I’m curious to hear whether you would like to see more of these evaluations and perhaps a comparison of the formats. If there isn’t much interest I likely won’t do more.

Muir Woods has one tree – plural issues in MediaWiki

Monday, October 29th, 2012

While I was having fun with the rest of the Wikimedia I18n team in San Francisco, a stream of plural related bug reports started coming in. The cause is that we have recently scrapped the custom plural rules in MediaWiki in favor of using plural rules from the CLDR database. A temporary fix has been applied to mitigate the reported issues.

The problem manifestation is pretty simple; in some languages in some contexts the message was always one something. For example the category page would say This category has one page regardless of how many pages there were in it. At first I was baffled. After all we had written unit tests for all languages in MediaWiki and they reported no regressions. Turns out we had ignored one particular set of languages: those which don’t always use plurals and had no plural rules defined in MediaWiki. The problems started when those language used plural even though they weren’t supposed to. When plural rules are not defined for a language, those languages use the plural rules as defined for the English language: 1 book, 2 books. In CLDR, however, some languages have been defined to not use any plural rules at all.

We could blame the translators for using plural syntax when they are not supported, or we could blame the CLDR for having no plurals rules for languages which do use plurals in some cases. It is not that simple, however. The typical example is a language which doesn’t have distinct plural forms (like some words in English: 1 fish, 2 fish; but for all nouns), but do use plural quantifiers if the number is not present: one fish, many fish.

As a compromise I have proposed an extension to the plural syntax to allow specifying the output when the number is 0 or 1 regardless of the usual plural rules for that language. Let’s take a real example:

Accepted by {{PLURAL:$1|you|$1 users including you}}.

This works fine in English, because the first form is always for number 1. In Belarusian it doesn’t work, because the first form is used for number 1, but also for numbers 21, 31, 41 etc. It could be solved by the following syntax:

{{PLURAL:$1|1=you|$1 users including you}}.

The slightly confusing part here is that now the second form is actually the singular form. This is more evident in the imaginary Belarus translation:


"you" is used for number 1, “one" for 21, 31, 41 but not 1, and the remaining forms as they usually are.

The explicit zero form (0=something) can also be useful for English and many other languages to have a different wording – something which is now usually done with separate messages.

The message used above is from the Translate extension. Unfortunately we cannot start using this syntax until we have dropped backwards compatibility with the last MediaWiki version not supporting  this syntax i.e. 1.20, which would be around when MediaWiki 1.22 is released. We are seriously considering to backport this functionality, but we also need to add support for the same syntax in JavaScript first.

During further testing we also found issues in Hebrew plural rules. The position of dual was changed and we didn’t notice it because the unit tests were wrong. This resulted in problems like the login page saying Remember my login for two days. It just helps reminding how bugs in i18n can cause potentially severe issues.

Niklas in Muir Woods.

Niklas in Muir Woods. Testing new counting methods? (Photo by Pau Giner.)

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