I18N::LangTags(3pPerl Programmers Reference GuiI18N::LangTags(3p)NAMEI18N::LangTags - functions for dealing with RFC3066-style
language tags
SYNOPSIS
use I18N::LangTags();
...or specify whichever of those functions you want to
import, like so:
use I18N::LangTags qw(implicate_supers similarity_language_tag);
All the exportable functions are listed below -- you're free
to import only some, or none at all. By default, none are
imported. If you say:
use I18N::LangTags qw(:ALL)
...then all are exported. (This saves you from having to
use something less obvious like "use I18N::LangTags
qw(/./)".)
If you don't import any of these functions, assume a
&I18N::LangTags:: in front of all the function names in the
following examples.
DESCRIPTION
Language tags are a formalism, described in RFC 3066
(obsoleting 1766), for declaring what language form
(language and possibly dialect) a given chunk of information
is in.
This library provides functions for common tasks involving
language tags as they are needed in a variety of protocols
and applications.
Please see the "See Also" references for a thorough explana-
tion of how to correctly use language tags.
* the function is_language_tag($lang1)
Returns true iff $lang1 is a formally valid language
tag.
is_language_tag("fr") is TRUE
is_language_tag("x-jicarilla") is FALSE
(Subtags can be 8 chars long at most -- 'jicarilla' is 9)
is_language_tag("sgn-US") is TRUE
(That's American Sign Language)
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is_language_tag("i-Klikitat") is TRUE
(True without regard to the fact noone has actually
registered Klikitat -- it's a formally valid tag)
is_language_tag("fr-patois") is TRUE
(Formally valid -- altho descriptively weak!)
is_language_tag("Spanish") is FALSE
is_language_tag("french-patois") is FALSE
(No good -- first subtag has to match
/^([xXiI]|[a-zA-Z]{2,3})$/ -- see RFC3066)
is_language_tag("x-borg-prot2532") is TRUE
(Yes, subtags can contain digits, as of RFC3066)
* the function extract_language_tags($whatever)
Returns a list of whatever looks like formally valid
language tags in $whatever. Not very smart, so don't
get too creative with what you want to feed it.
extract_language_tags("fr, fr-ca, i-mingo")
returns: ('fr', 'fr-ca', 'i-mingo')
extract_language_tags("It's like this: I'm in fr -- French!")
returns: ('It', 'in', 'fr')
(So don't just feed it any old thing.)
The output is untainted. If you don't know what taint-
ing is, don't worry about it.
* the function same_language_tag($lang1, $lang2)
Returns true iff $lang1 and $lang2 are acceptable vari-
ant tags representing the same language-form.
same_language_tag('x-kadara', 'i-kadara') is TRUE
(The x/i- alternation doesn't matter)
same_language_tag('X-KADARA', 'i-kadara') is TRUE
(...and neither does case)
same_language_tag('en', 'en-US') is FALSE
(all-English is not the SAME as US English)
same_language_tag('x-kadara', 'x-kadar') is FALSE
(these are totally unrelated tags)
same_language_tag('no-bok', 'nb') is TRUE
(no-bok is a legacy tag for nb (Norwegian Bokmal))
"same_language_tag" works by just seeing whether
"encode_language_tag($lang1)" is the same as
"encode_language_tag($lang2)".
(Yes, I know this function is named a bit oddly. Call
it historic reasons.)
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* the function similarity_language_tag($lang1, $lang2)
Returns an integer representing the degree of similarity
between tags $lang1 and $lang2 (the order of which does
not matter), where similarity is the number of common
elements on the left, without regard to case and to x/i-
alternation.
similarity_language_tag('fr', 'fr-ca') is 1
(one element in common)
similarity_language_tag('fr-ca', 'fr-FR') is 1
(one element in common)
similarity_language_tag('fr-CA-joual',
'fr-CA-PEI') is 2
similarity_language_tag('fr-CA-joual', 'fr-CA') is 2
(two elements in common)
similarity_language_tag('x-kadara', 'i-kadara') is 1
(x/i- doesn't matter)
similarity_language_tag('en', 'x-kadar') is 0
similarity_language_tag('x-kadara', 'x-kadar') is 0
(unrelated tags -- no similarity)
similarity_language_tag('i-cree-syllabic',
'i-cherokee-syllabic') is 0
(no B<leftmost> elements in common!)
* the function is_dialect_of($lang1, $lang2)
Returns true iff language tag $lang1 represents a sub-
form of language tag $lang2.
Get the order right! It doesn't work the other way
around!
is_dialect_of('en-US', 'en') is TRUE
(American English IS a dialect of all-English)
is_dialect_of('fr-CA-joual', 'fr-CA') is TRUE
is_dialect_of('fr-CA-joual', 'fr') is TRUE
(Joual is a dialect of (a dialect of) French)
is_dialect_of('en', 'en-US') is FALSE
(all-English is a NOT dialect of American English)
is_dialect_of('fr', 'en-CA') is FALSE
is_dialect_of('en', 'en' ) is TRUE
is_dialect_of('en-US', 'en-US') is TRUE
(B<Note:> these are degenerate cases)
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is_dialect_of('i-mingo-tom', 'x-Mingo') is TRUE
(the x/i thing doesn't matter, nor does case)
is_dialect_of('nn', 'no') is TRUE
(because 'nn' (New Norse) is aliased to 'no-nyn',
as a special legacy case, and 'no-nyn' is a
subform of 'no' (Norwegian))
* the function super_languages($lang1)
Returns a list of language tags that are superordinate
tags to $lang1 -- it gets this by removing subtags from
the end of $lang1 until nothing (or just "i" or "x") is
left.
super_languages("fr-CA-joual") is ("fr-CA", "fr")
super_languages("en-AU") is ("en")
super_languages("en") is empty-list, ()
super_languages("i-cherokee") is empty-list, ()
...not ("i"), which would be illegal as well as pointless.
If $lang1 is not a valid language tag, returns empty-
list in a list context, undef in a scalar context.
A notable and rather unavoidable problem with this
method: "x-mingo-tom" has an "x" because the whole tag
isn't an IANA-registered tag -- but
super_languages('x-mingo-tom') is ('x-mingo') -- which
isn't really right, since 'i-mingo' is registered. But
this module has no way of knowing that. (But note that
same_language_tag('x-mingo', 'i-mingo') is TRUE.)
More importantly, you assume at your peril that superor-
dinates of $lang1 are mutually intelligible with $lang1.
Consider this carefully.
* the function locale2language_tag($locale_identifier)
This takes a locale name (like "en", "en_US", or
"en_US.ISO8859-1") and maps it to a language tag. If
it's not mappable (as with, notably, "C" and "POSIX"),
this returns empty-list in a list context, or undef in a
scalar context.
locale2language_tag("en") is "en"
locale2language_tag("en_US") is "en-US"
locale2language_tag("en_US.ISO8859-1") is "en-US"
locale2language_tag("C") is undef or ()
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locale2language_tag("POSIX") is undef or ()
locale2language_tag("POSIX") is undef or ()
I'm not totally sure that locale names map satisfac-
torily to language tags. Think REAL hard about how you
use this. YOU HAVE BEEN WARNED.
The output is untainted. If you don't know what taint-
ing is, don't worry about it.
* the function encode_language_tag($lang1)
This function, if given a language tag, returns an
encoding of it such that:
* tags representing different languages never get the
same encoding.
* tags representing the same language always get the
same encoding.
* an encoding of a formally valid language tag always is
a string value that is defined, has length, and is true
if considered as a boolean.
Note that the encoding itself is not a formally valid
language tag. Note also that you cannot, currently, go
from an encoding back to a language tag that it's an
encoding of.
Note also that you must consider the encoded value as
atomic; i.e., you should not consider it as anything but
an opaque, unanalysable string value. (The internals of
the encoding method may change in future versions, as
the language tagging standard changes over time.)
"encode_language_tag" returns undef if given anything
other than a formally valid language tag.
The reason "encode_language_tag" exists is because dif-
ferent language tags may represent the same language;
this is normally treatable with "same_language_tag", but
consider this situation:
You have a data file that expresses greetings in dif-
ferent languages. Its format is "[language tag]=[how to
say 'Hello']", like:
en-US=Hiho
fr=Bonjour
i-mingo=Hau'
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And suppose you write a program that reads that file and
then runs as a daemon, answering client requests that
specify a language tag and then expect the string that
says how to greet in that language. So an interaction
looks like:
greeting-client asks: fr
greeting-server answers: Bonjour
So far so good. But suppose the way you're implementing
this is:
my %greetings;
die unless open(IN, "<in.dat");
while(<IN>) {
chomp;
next unless /^([^=]+)=(.+)/s;
my($lang, $expr) = ($1, $2);
$greetings{$lang} = $expr;
}
close(IN);
at which point %greetings has the contents:
"en-US" => "Hiho"
"fr" => "Bonjour"
"i-mingo" => "Hau'"
And suppose then that you answer client requests for
language $wanted by just looking up $greetings{$wanted}.
If the client asks for "fr", that will look up success-
fully in %greetings, to the value "Bonjour". And if the
client asks for "i-mingo", that will look up success-
fully in %greetings, to the value "Hau'".
But if the client asks for "i-Mingo" or "x-mingo", or
"Fr", then the lookup in %greetings fails. That's the
Wrong Thing.
You could instead do lookups on $wanted with:
use I18N::LangTagsqw(same_language_tag);
my $repsonse = '';
foreach my $l2 (keys %greetings) {
if(same_language_tag($wanted, $l2)) {
$response = $greetings{$l2};
last;
}
}
But that's rather inefficient. A better way to do it is
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to start your program with:
use I18N::LangTagsqw(encode_language_tag);
my %greetings;
die unless open(IN, "<in.dat");
while(<IN>) {
chomp;
next unless /^([^=]+)=(.+)/s;
my($lang, $expr) = ($1, $2);
$greetings{
encode_language_tag($lang)
} = $expr;
}
close(IN);
and then just answer client requests for language
$wanted by just looking up
$greetings{encode_language_tag($wanted)}
And that does the Right Thing.
* the function alternate_language_tags($lang1)
This function, if given a language tag, returns all
language tags that are alternate forms of this language
tag. (I.e., tags which refer to the same language.)
This is meant to handle legacy tags caused by the minor
changes in language tag standards over the years; and
the x-/i- alternation is also dealt with.
Note that this function does not try to equate new (and
never-used, and unusable) ISO639-2 three-letter tags to
old (and still in use) ISO639-1 two-letter equivalents
-- like "ara" -> "ar" -- because "ara" has never been in
use as an Internet language tag, and RFC 3066 stipulates
that it never should be, since a shorter tag ("ar")
exists.
Examples:
alternate_language_tags('no-bok') is ('nb')
alternate_language_tags('nb') is ('no-bok')
alternate_language_tags('he') is ('iw')
alternate_language_tags('iw') is ('he')
alternate_language_tags('i-hakka') is ('zh-hakka', 'x-hakka')
alternate_language_tags('zh-hakka') is ('i-hakka', 'x-hakka')
alternate_language_tags('en') is ()
alternate_language_tags('x-mingo-tom') is ('i-mingo-tom')
alternate_language_tags('x-klikitat') is ('i-klikitat')
alternate_language_tags('i-klikitat') is ('x-klikitat')
This function returns empty-list if given anything other
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than a formally valid language tag.
langs = panic_languages(@accept_languages)@u-3p
* the function @langs = panic_languages(@accept_languages)
This function takes a list of 0 or more language tags
that constitute a given user's Accept-Language list, and
returns a list of tags for other (non-super) languages
that are probably acceptable to the user, to be used if
all else fails.
For example, if a user accepts only 'ca' (Catalan) and
'es' (Spanish), and the documents/interfaces you have
available are just in German, Italian, and Chinese, then
the user will most likely want the Italian one (and not
the Chinese or German one!), instead of getting nothing.
So "panic_languages('ca', 'es')" returns a list contain-
ing 'it' (Italian).
English ('en') is always in the return list, but whether
it's at the very end or not depends on the input
languages. This function works by consulting an inter-
nal table that stipulates what common languages are
"close" to each other.
A useful construct you might consider using is:
@fallbacks = super_languages(@accept_languages);
push @fallbacks, panic_languages(
@accept_languages, @fallbacks,
);
* the function implicate_supers( ...languages... )
This takes a list of strings (which are presumed to be
language-tags; strings that aren't, are ignored); and
after each one, this function inserts super-ordinate
forms that don't already appear in the list. The origi-
nal list, plus these insertions, is returned.
In other words, it takes this:
pt-br de-DE en-US fr pt-br-janeiro
and returns this:
pt-br pt de-DE de en-US en fr pt-br-janeiro
This function is most useful in the idiom
implicate_supers( I18N::LangTags::Detect::detect() );
(See I18N::LangTags::Detect.)
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* the function implicate_supers_strictly( ...languages... )
This works like "implicate_supers" except that the
implicated forms are added to the end of the return
list.
In other words, implicate_supers_strictly takes a list
of strings (which are presumed to be language-tags;
strings that aren't, are ignored) and after the whole
given list, it inserts the super-ordinate forms of all
given tags, minus any tags that already appear in the
input list.
In other words, it takes this:
pt-br de-DE en-US fr pt-br-janeiro
and returns this:
pt-br de-DE en-US fr pt-br-janeiro pt de en
The reason this function has "_strictly" in its name is
that when you're processing an Accept-Language list
according to the RFCs, if you interpret the RFCs quite
strictly, then you would use implicate_supers_strictly,
but for normal use (i.e., common-sense use, as far as
I'm concerned) you'd use implicate_supers.
ABOUT LOWERCASING
I've considered making all the above functions that output
language tags return all those tags strictly in lowercase.
Having all your language tags in lowercase does make some
things easier. But you might as well just lowercase as you
like, or call "encode_language_tag($lang1)" where appropri-
ate.
ABOUT UNICODE PLAINTEXT LANGUAGE TAGS
In some future version of I18N::LangTags, I plan to include
support for RFC2482-style language tags -- which are basi-
cally just normal language tags with their ASCII characters
shifted into Plane 14.
SEE ALSO
* I18N::LangTags::List
* RFC 3066, "ftp://ftp.isi.edu/in-notes/rfc3066.txt", "Tags
for the Identification of Languages". (Obsoletes RFC 1766)
* RFC 2277, "ftp://ftp.isi.edu/in-notes/rfc2277.txt", "IETF
Policy on Character Sets and Languages".
* RFC 2231, "ftp://ftp.isi.edu/in-notes/rfc2231.txt", "MIME
Parameter Value and Encoded Word Extensions: Character Sets,
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Languages, and Continuations".
* RFC 2482, "ftp://ftp.isi.edu/in-notes/rfc2482.txt",
"Language Tagging in Unicode Plain Text".
* Locale::Codes, in
"http://www.perl.com/CPAN/modules/by-module/Locale/"
* ISO 639-2, "Codes for the representation of names of
languages", including two-letter and three-letter codes,
"http://www.loc.gov/standards/iso639-2/langcodes.html"
* The IANA list of registered languages (hopefully
up-to-date), "http://www.iana.org/assignments/language-tags"
COPYRIGHT
Copyright (c) 1998+ Sean M. Burke. All rights reserved.
This library is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.
The programs and documentation in this dist are distributed
in the hope that they will be useful, but without any war-
ranty; without even the implied warranty of merchantability
or fitness for a particular purpose.
AUTHOR
Sean M. Burke "sburke@cpan.org"
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