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Mathew Robertson > Locale-MakePhrase > Locale::MakePhrase::OSDC2004


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This POD is a conference paper for the OpenSource Developers Conference 2004 (Melbourne, Australia).

The information that follows is description of a technique which is in use within the Locale::MakePhrase module.


Language localisation of applications (ie internationalisation of text strings) can be a complicated problem. Existing solutions are often based around enumerating or objectifying the message, thus allowing the output mechanism to display the appropriate string. Alternatively, we can use a text string as a key to a mechanism which returns the language specific string.

Most translation systems are loosely based around one of these concepts. For example, the C library implements the catgets function (among many locale-related functions), which takes a 'message number' and returns a string based on the language. The gettext function call implements a similar mechanism.

The following information describes a Perl module which implements a (possibly new?) technique which I have termed linguistic rule evaluation, ie language rules which can be evaluated at run-time. Using this technique, it is possible to determine which language phrase to be output, given the current input phrase.

Note that this module still requires a linguist to mark-up the application (in the appropriate language/dialect), except that it provides a more sophisticated set of tools (than say, gettext) so that when some text gets displayed, it will more accurately reflect the application context.

For further information on the complexities of localising application strings, please read Locale::Maketext::TPJ13.

How would you or I speak a phrase in a second language? ^

Many people speak more than one language. When a person wants to translate a phrase from one language to another, they will usually do something like:

  1. Think of the phrase that you want to say, usually in the language that they speak most often.
  2. Try to understand what it is they are trying to say; that is, they determine the context/meaning of the phrase.
  3. Speak that information in the second language.

The important point is that the information conveyed by the phrase is what is being translated, and this is determined by all of the various pieces of information surrounding the phrase (such as, the geographical region).

How hard is it really? ^

Luckily for us, linguists already have a pretty good idea of how to translate any given phrase, into a second language. Actually, so does anyone that can speak more than one language...

The general philosophy is that for phrases that dont have any of the 'fill in the blanks' (as in "Please choose some ___"), then it is a relatively simple problem to translate the phrase; its generally just a matter of knowing the language/region (as in en_au).

However, for the 'fill in the blanks' phrases, then it is substantially more complicated, as we have to handle singular, plural, duality, zero, etc. on a per-language basis.

But more importantly, each blank that needs to be filled, needs to be tested to understand what what information it is actually trying to convey. For example:

Lets say that the English phrase is "Please select ___ files", where the blank entry is a number. And lets assume that we would like to display the correct output phrase which matches the 'meaning' of the phrase for all possible values of blank.

Now, if the blank has a value of zero then ideally we would like to be able to display "Dont select any files". To output this phrase we need to evaluate the value of the blank; if the value is non-zero, then we would want to display something else.

This test/evaluation needs to happen at run-time, as the value of the blank is not known until just before we output the message; and this example is just for English - lets extrapolate this a little bit...

What if the blank has a value of one? Ideally we want to output the phrase "Only select a single file".

What if the value is two? Should we output "Please select 2 files" or should we output "Please select two files"?

What happens if the value is really big? What happens if it negative?

This example is applicable for English. What about the next language? Do any of these tests/evaluations apply? If so, how many of these tests are common to all languages?


I have just said "the no-fill-in-the-blanks" is relatively simple, in the translation stages. However, this ignores the fact that phrases in some languages also have gender, age, seniority and other properties that should be taken into account. This is the subject of further study.

Don't assume a property of one language, is applicable to others. ^

The previous example highlighted the number of phrases that need evaluation for English. It turns out that assuming other languages have similar properties, is simply a misnomer; there is no single person who would be capable of understanding the nuances of every language. Thus it is pointless to even try to make a property of one language, also apply to another.

Lets look at an example - Chinese vs English.

When translating a phrase with numbers, in most cases the Chinese phrase wont change for the singular vs plural cases.

Whereas Engligh requires two seperate phrases, one for singular and one for plural.

What is a linguistic rule? ^

Now that we have discussed how you or I would translate a phrase, lets explain the concept of a linguistic rule.

A linguistic rule contains the properties to encapsulate the technique of interpreting the meaning of a phrase. When we want to translate a given phrase into another language, we select the most appropriate rule from many rules. The choice of the most suitable rules, is part of the linuguistic rule evaluation engine.

A rule has the following properties:


This is an RFC3066 language tag (eg 'en' or 'en_au').


This is the phrase that is used as the base input phrase. This will most likely be in the language of the programmer (eg English).


The output phrase written in the appropriate language.


If the phrase contains variables, this is the expression that is used to determine if this output phrase should be the phrase that is chosen.


In some circumstances, there may be multiple expressions which evaluate to be true. The priority is used to determine which expression to evaluate first.

A linguistic rule, from programmers point of view, is a struct which contains enough information to enable us to implement an equivalent process as that of a linguist.

Text syntax ^

Before we describe some of the details, we should explain the syntax of the application text.

Whenever we want an application value to take part in the phrase, we use the syntax:

  "This is some phrase, with a [_1] value that is to be run-time evaluated"

The square brackets indicate that a program value is going to be passed to the translation engine. Some application strings dont have any program arguements, while others will have many.

Expression syntax ^

The sytax of an expression, is of the form:

  _X op val


  X   - numerical application argument; the underscore indicates
        that the value is an argument, not a value
  op  - evaluation operator
  val - the value to tested against

An example of an expression, for English:

  _1 == 0
  _2 > 1
  left(_3,5) eq "house"

Linguistic rule evaluation ^

To summarise, the engine implements the following:

  1. Find all language rules where the key matches the input phrase, for the corresponding language tag. Note that the implementation supports the concept of fallback languages (eg: 'en_au' falls back to 'en'). The linguistic rules for the fallback languages which match the key, are also retrieved.
  2. Sort the rules based on a combination of the priority, the language tag (eg 'en_au' has higher precedence than 'en') and whether a non-null expression exists. Rules with no expression have the lowest priority.
  3. Evalute the expression from each rule, starting with the highest priority. The first rule to evaluate to true, is chosen.
  4. Apply the arguments in-place, to the selected rule's translated value.

Features ^

Example ^

The Locale::MakePhrase tarball contains test cases. These are used as working examples...

Further development ^

Gender... Age...

As an examples, lets say that we were talking about a person, specifically a female child. In Italian the term used would be 'bambina'; for a male child it is 'bambino'. Thus in this case, the context surrounding the phrase will include the age and gender of the child.

How do we handle this? Future development may revolve around the support of gender, age and seniority.

Each of these three properties need to be considered from the point of view of the speaker as well as the receiver. Since the speaker is simply a computer, one possible scenario is to pass the age and gender of the user, as arguments to the constructor of the translation instance.

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