I18N::LangTags(3p) Perl Programmers Reference Guide I18N::LangTags(3p)

I18N::LangTags(3p) Perl Programmers Reference Guide I18N::LangTags(3p) #

I18N::LangTags(3p) Perl Programmers Reference Guide I18N::LangTags(3p)

NNAAMMEE #

 I18N::LangTags - functions for dealing with RFC3066-style language tags

SSYYNNOOPPSSIISS #

   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.

DDEESSCCRRIIPPTTIIOONN #

 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 explanation 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)

        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 tainting is, don't
     worry about it.

 •   the function same_language_tag($lang1, $lang2)

     Returns true iff $lang1 and $lang2 are acceptable variant 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.)

 •   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 subform of language
     tag $lang2.

     GGeett tthhee oorrddeerr rriigghhtt!!  IItt ddooeessnn''tt wwoorrkk tthhee ootthheerr wwaayy aarroouunndd!!

        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)

        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 _a_t _y_o_u_r _p_e_r_i_l that superordinates 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 ()

        locale2language_tag("POSIX") is undef or ()

        locale2language_tag("POSIX") is undef or ()

     I'm not totally sure that locale names map satisfactorily 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 tainting 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 nnoott 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 mmuusstt 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 different 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 different languages.
     Its format is "[language tag]=[how to say 'Hello']", like:

               en-US=Hiho
               fr=Bonjour
               i-mingo=Hau'

     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 successfully in
     %greetings, to the value "Bonjour".  And if the client asks for
     "i-mingo", that will look up successfully 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::LangTags qw(same_language_tag);
               my $response = '';
               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 to start
     your program with:

               use I18N::LangTags qw(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 _n_o_t 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 _n_e_v_e_r 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 than a
     formally valid language tag.

 •   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
     _o_t_h_e_r (non-super) languages that are probably acceptable to the user,
     to be used _i_f _a_l_l _e_l_s_e _f_a_i_l_s.

     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
     containing 'it' (Italian).

     English ('en') is _a_l_w_a_y_s 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 internal 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 original 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.)

 •   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.

AABBOOUUTT LLOOWWEERRCCAASSIINNGG #

 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
 appropriate.

AABBOOUUTT UUNNIICCOODDEE PPLLAAIINNTTEEXXTT LLAANNGGUUAAGGEE TTAAGGSS #

 In some future version of I18N::LangTags, I plan to include support for
 RFC2482-style language tags -- which are basically just normal language
 tags with their ASCII characters shifted into Plane 14.

SSEEEE AALLSSOO #

 * I18N::LangTags::List

 * RFC 3066, "<http://www.ietf.org/rfc/rfc3066.txt>", "Tags for the
 Identification of Languages".  (Obsoletes RFC 1766)

 * RFC 2277, "<http://www.ietf.org/rfc/rfc2277.txt>", "IETF Policy on
 Character Sets and Languages".

 * RFC 2231, "<http://www.ietf.org/rfc/rfc2231.txt>", "MIME Parameter
 Value and Encoded Word Extensions: Character Sets, Languages, and
 Continuations".

 * RFC 2482, "<http://www.ietf.org/rfc/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/php/code_list.php>"

 * The IANA list of registered languages (hopefully up-to-date),
 "<http://www.iana.org/assignments/language-tags>"

CCOOPPYYRRIIGGHHTT #

 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 warranty; without even the
 implied warranty of merchantability or fitness for a particular purpose.

AAUUTTHHOORR #

 Sean M. Burke "sburke@cpan.org"

perl v5.36.3 2023-02-15 I18N::LangTags(3p)