[Bug locale/20184] New: API for language priority list

[ueno at gnu dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=20184

            Bug ID: 20184
           Summary: API for language priority list
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: locale
          Assignee: unassigned at sourceware dot org
          Reporter: ueno at gnu dot org
  Target Milestone: ---

While discussing on potentially thread-unsafe getenv() call in gettext() for
LANGUAGE, Bruno Haible suggested to add an API that is equivalent to the envvar
setting, in a lower layer than gettext():
https://lists.gnu.org/archive/html/bug-gettext/2016-05/msg00009.html

At first it seems a bit overkill to me though (because the only user is
currently gettext()), the concept itself seems not uncommon: W3C ltli[1]
defines the term "language priority list" and ICU4J provides a class
LocalePriorityList[2] so multilingual applications might benefit from the API.

My current suggestion is to add the following two functions to
<locale.h> as a GNU extension:

  /* Sets the language priority list for the calling thread to LANGUAGES.

     LANGUAGES may be a colon-separated list of language codes.
     If LANGUAGES is NULL, use the one inferred from the environment
     variable 'LANGUAGE'.

     The effect of the language priority list is application
     dependent.  However, supporting applications should give
     priority to the language priority list over the locale
     settings.

     This returns an opaque string that corresponds to the current
     language priority list.  */
  const char *
  set_language_priority_list (const char *languages);

  /* Returns the language priority list for the calling thread.

     This returns NULL if the list is not set yet, or an opaque string
     that corresponds to the current language priority list.  */
  const char *
  get_language_priority_list (void);

[1] https://www.w3.org/TR/ltli/
[2]
http://icu-project.org/apiref/icu4j/com/ibm/icu/util/LocalePriorityList.html

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