Goals of this project is:

• To be more or less compatible with GNU gettext (API and tools).
• To be as fast as possible in concurrent environment.

You may use this app to translate libraries as well as your own business apps and use them in single installation with no conflicts. Libraries may ship their own translations inside their distribution.

You definitely should be familiar with GNU gettext before start using this library.

In Erlang code include shortcuts.hrl header file.

-include_lib("gettexter/include/shortcuts.hrl").

Mark your translatable strings with:

• ?_("") - gettext (regular)
• ?N_("", "", N) - ngettext (plural)
• ?P_(Ctx, "") - pgettext (respecting msgctx)
• ?NP_(Ctx, "", "", N) - npgettext (ngettext + pgettext)
• ?D_(Domain, "") - dgettext (domain/namespace lookups, plus ?DN_, ?DP_, ?DNP_)
• ?NO_("") - gettext noop

% file: my_app/src/my_module.erl
-module(my_module).
-define(GETTEXT_DOMAIN, my_app).
-include_lib("gettexter/include/shortcuts.hrl").

main(Name, What, N) ->
    gettexter:bindtextdomain(?GETTEXT_DOMAIN, "/../priv/locales"), % from where load locales
    gettexter:textdomain(?GETTEXT_DOMAIN), % domain for current process
    gettexter:setlocale(lc_messages, "en"),  % locale for current process

    Question = case What of
                 sleep -> ?NO_("Wanna sleep?");
                 eat -> ?NO_("Wanna eat?")
               end,
    Time = io_lib:format(?N_("It's ~p hour", "It's ~p hours", N), [N]),
    %% /* Translators: this is hello message */
    io:format(?_("Hello, ~p! ~ts. ~ts"), [Name, Time, ?_(Question)]).

Extract messages from sources to .pot file by xgettext command. Take note that this only work for string literals and not binaries.

export APP=my_app

xgettext -o priv/locale/${APP}.pot --package-name=${APP} -d ${APP} --sort-by-file -L C \
    --keyword='NO_' --keyword='_' --keyword='N_:1,2' \
    --keyword='P_:1c,2' --keyword='NP_:1c,2,3' \
    --keyword='D_:2' --keyword='DN_:2,3' --keyword='DP_:2c,3' --keyword='DNP_:2c,3,4' \
    --add-comments=Translators \
    src/my_module.erl src/*.erl

Initialize new locale's .po file by msginit

mkdir -p priv/locale/ru/LC_MESSAGES/
msginit -i priv/locale/${APP}.pot -o priv/locale/ru/LC_MESSAGES/${APP}.po --locale=ru

Or actualize existing locale's .po file by msgmerge

msgmerge -U priv/locale/ru/LC_MESSAGES/${APP}.po priv/locale/${APP}.pot

When translations are finished, generate locale's binary .mo files by msgfmt

msgfmt --check -o priv/locale/ru/LC_MESSAGES/${APP}.mo priv/locale/ru/LC_MESSAGES/${APP}.po

It's strongly recommended to not add .mo files to your repository! So, add *.mo to .gitignore / .hgignore and generate them in compile-time (by rebar post-compile hook or so).

Api tries to be compatible with GNU gettext API. If you find some discrepancy (not explicitly documented) - please report.

All lookup functions are able to take both binaries or strings. They will return what is given to them. Mixed textual types is not supported.

Each lookup function and macros has it's arity + 1 companion, which accept explicit locale as last argument. So, gettexter:gettext(text()) has gettexter:gettext(text(), locale()), ?_(text()) has ?_(text(), locale()) and so on.

For more information see the documentation.

gettexter:gettext(text()) -> text().  % '?_' macro

Main gettext call. Uses locale, activated by setlocale/2.

gettexter:ngettext(Singular :: text(), Plural :: text(),
                   Count :: integer()) -> text().  % '?N_' macro

Plural gettext call.

gettexter:pgettext(Context :: text(), text()) -> text().  % '?P_'
gettexter:pngettext(Context :: text(), text(), text(),
                    integer()) -> text().  % '?PN_'

Gettext calls with respect to msgctx ('p' means 'particular').

gettexter:dgettext(Domain :: atom(), text()) -> text().  % '?D_'
% and other 'gettexter:d{n,p,pn}gettext' plus '?D*_' macroses

Gettext calls, which will search in a specific domain (namespace). (See bindtextdomain).

gettexter:bindtextdomain(Domain :: atom(), LocaleDir :: file:filename()) -> ok.

Setup directory from which .mo files will be loaded like ${LocaleDir}/${Locale}/LC_MESSAGES/${Domain}.mo. Domain MUST be specified for library applications (see dgettext).

By default, Domain is application:get_application() and LocaleDir is filename:absname(filename:join(code:priv_dir(Domain), "locale")). If LocaleDir is relative, absolute path will be calculated, unlike original gettext does (relative to cwd), but relative to code:priv_dir(Domain).

This function don't reload already loaded locales for Domain, so, should be called before setlocale or ensure_loaded calls.

This function usualy called only once at application initialization/configuration phase.

gettexter:setlocale(lc_messages, Locale :: text()) -> ok.
gettexter:getlocale(lc_messages) -> text() | undefined.

Get / Set default locale for current process. It also loads .mo files for Locale from the LocaleDirs for each Domain (if not loaded yet). 1'st argumet currently has only one value - lc_messages atom. Note: getlocale is not standard GNU gettext function.

gettexter:textdomain() -> atom() | undefined.
gettexter:textdomain(Domain :: atom()) -> ok.

Get/Set default domain (namespace) for current process. If you call it like textdomain(my_app), then gettext(Key) calls will be converted to dgettext(my_app, Key). XXX: it's highly preferable to use dgettext directly and don't use this API function, if localized strings can be rendered in different processes.

gettexter:bind_textdomain_codeset(Domain :: atom(), Charset :: string()) -> ok.

Set encoding, on which all gettexter:*gettext responses should be converted. This add significant performance overhead, and require 'iconv' dependency, if .po file's Content-Type and Charset isn't the same.

XXX: Note, that gettexter:gettext(Key) call will be finally converted to gettexter:dpgettext(undefined, undefined, Key), which will try to extract Domain and Locale from current process dictionary.

XXX: When developing library, you may want to re-define ?_, ?N_, ?P_ macroses to call dgettext and use your module's domain by default. You can do this by following trick:

-define(GETTEXT_DOMAIN, my_domain).
-include_lib("gettexter/include/shortcuts.hrl").

This will modify macroses (except ?_D*) to use d*gettext(my_domain, ...) by default.

This apis has no GNU gettext equiualents, but may be useful in Erlang apps.

gettexter:which_domains(Locale) -> [atom()].

Which domains are loaded from .mo files to gettext server for Locale.

gettexter:which_locales(Domain) -> [locale()].

Which locales are loaded from .mo files to gettext server for Domain.

gettexter:ensure_loaded(TextDomain, lc_messages, Locale) ->
    {ok, already} | {ok, MoFile :: file:filename()} | {error, term()}.

Ensure, that locale is loaded from .mo file to gettexter server. If locale isn't loaded, all gettext lookups to it will return default value Msgid. This function may be called at application start-up or configuration time, once for each supported locale. In case of error, all data for this combination of Domain and Locale will be removed from gettexter server to avoid incomplete/broken data.

reload(Domain) -> list().

reload(Domain, [locale()]) -> [{locale(), ok, file:filename()} |
                               {locale(), error, any()}].

Re-reads the phrases from .mo files bound by bindtextdomain/2 (eg, if those files changed). Function reload/1 reloads ALL the locales of the domain Domain.

gettexter:reset() -> ok.

Remove all gettext stuff, added by setlocale or textdomain, from process dictionary (but not from locale data storage). May be used to reuse process for the next client.

• Domain: namespace for translations. In practice, the name of .po/.mo file, which in most cases, named as your OTP application.
• Locale: not strictly speaking, just name of translation's language, like "en", "en_GB", "ru", "pt_BR", etc. Usualy Locale contains also rules of plural form calculation, date/time/number formatting, currency etc.
• LC_MESSAGES: locale category, which contains translated application's strings (in .mo/.po format).

Erlydtl >= 0.9.4 supports plural forms and contexts. So, you can use all gettexter features with it. To enable translation features of erlydtl, you should wrap all translatable strings in {%trans%}, {%blocktrans%} and _(), generate .po and .mo files and then pass translation_fun and locales in compile-time, or translation_fun and locale in render-time.

Example translation_fun:

TransFun = fun({Str, {StrPlural, N}}, {Locale, Ctx}) ->
               gettexter:pngettext(Ctx, Str, StrPlural, N, Locale);
              ({Str, {StrPlural, N}}, Locale) ->
               gettexter:ngettext(Str, StrPlural, N, Locale);
              (Str, {Locale, Ctx}) ->
               gettexter:pgettext(Ctx, Str, Locale);
              (Str, Locale) ->
               gettexter:gettext(Str, Locale)
           end.

Template:

{# file: src/tpl.dtl #}
{%trans "Hello"%}
{%trans "Hello" context "ctx"%}
{% blocktrans count cnt=cnt %}Apple{%plural%}Apples{%endblocktrans%}

.po file

#file: priv/locale/ru/LC_MESSAGES/test_app.po + compiled .mo
msgid ""
msgstr ""
"Content-Type: text/plain; charset=utf-8\n"
"Plural-Forms: nplurals=3; plural=n%10==1 && n%100!=11 ? 0 : n%10>=2 && n"
"%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2;\n"

msgid "Hello"
msgstr "Привет"

msgctxt "ctx"
msgid "Hello"
msgstr "Контекстный привет"

msgid "Apple"
msgid_plural "Apples"
msgstr[0] "Яблоко"
msgstr[1] "Яблока"
msgstr[2] "Яблок"

Code:

1> application:start(gettexter).
2> Domain = test_app.
3> % next step may be skipped, if `code:priv_dir(Domain)` is ok (if Domain is appname)
3> gettexter:bindtextdomain(Domain, </path/to/app/priv> ++ "/locale").
4> gettexter:textdomain(Domain).
5> erlydtl:compile_file("src/tpl.dtl", t).
6> TransFun = '....'. % see above
7> {ok, R} = t:render(),  io:format("~ts~n", [iolist_to_binary(R)]).
Hello
Hello

Apple
8> {ok, R1} = t:render([{cnt, 2}], [{locale, "ru"}, {translation_fun, TransFun}]).
9> io:format("~ts~n", [iolist_to_binary(R1)]).
Привет
Контекстный привет

Яблока

Expression, ?_(<<"...">>) is not well handled by xgettext, so, variants:

• Use ?NO_ hack: Key = <<?NO_("text")>>, Translated = ?_(Key)

• Write own extractor like xgettext, but for erlang code. Also, .pot serializer will be needed then.

• Send patches to GNU gettext.

Maybe allow bindtextdomain/2 2'nd argument be a {M, F, A} or fun M:F/N to allow locale loading customization?

Since ETS lookups require heap copying, smth like static .beam module with compiled-in phrases and plural rules (!!!) may be generated. Pros: extra fast access speed; no memory copying; compiled plural rules. Cons: slow update; hackish.