I18n strategies for Go with App Engine

Question

Not necessarily specific to GAE I suppose, but I'm curious as to what people are using to translate or localise their web applications.

My own approach I'm afraid is hopelessly naive, really just a hand-wave at the issue by loading an entity from the datastore for each package based on a locale value recorded in the user's profile. At least this allows translations of a few strings to be provided:

package foo

...

type Messages struct {
    Locale string
    ErrorDatastore string
    LoginSuccessful string
    ...
}

Store with a string id corresponding to a locale, then load to Gorilla context or similar:

const Messages ContextKey = iota

...

k := datastore.NewKey(c, "Messages", "en_US", 0, nil)
m := new(Messages)
if err := datastore.Get(c, k, m); err != nil {
    ...
} else {
    context.Set(r, Messages, m)
}

Which is obviously incredibly limited, but at least makes strings available from calling code via context.Get(r, foo.Messages). Can anyone point me at more useful implementations, or suggest a better approach?

Edit (relevant but not completely useful):

• gettext: a MO file parser
• go-18n
• Internationalization plan for Go
• Polyglot

Answer 1

Jonathan Chan points out Samuel Stauffer's go-gettext which seems to do the trick. Given the directories:

~appname/
 |~app/
 | `-app.go
 |+github.com/
 `-app.yaml

Start with (assumes *nix):

$ cd appname
$ git clone git://github.com/samuel/go-gettext.git github.com/samuel/go-gettext

Source preparation cannot use the _("String to be translated") short form, due to underscore's special characteristics in Go. You can tell xgettext to look for the camelcase function name "GetText" using the -k flag.

Minimal working example:

package app

import (
    "fmt"
    "log"
    "net/http"

    "github.com/samuel/go-gettext"
)

func init () {
    http.HandleFunc("/", home)
}

func home(w http.ResponseWriter, r *http.Request) {
    d, err := gettext.NewDomain("appname", "locale")
    if err != nil {
        log.Fatal("Failed at NewDomain.")
    }

    cat := d.GetCatalog("fr_FR")
    if cat == gettext.NullCatalog {
        log.Fatal("Failed at GetCatalog.")
    }

    fmt.Fprintf(w, cat.GetText("Yes."))
}

Create the template with:

$ xgettext -d appname -kGetText -s -o appname.pot app/app.go

Note -k, without it there'll be no output as xgettext won't recognise calls to GetText. Edit relevant strings, email etc in appname.pot. Let's assume we're localising for French:

$ mkdir -p locale/fr_FR/LC_MESSAGES
$ msginit -l fr_FR -o french.po -i appname.pot

Edit french.po:

# Appname l10n
# Copyright (C) 2013 Wombat Inc
# This file is distributed under the same license as the appname package.
# Wombat <[email protected]>, 2013.
#
msgid ""
msgstr ""
"Project-Id-Version: appname v0.1\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2013-01-13 11:03+1300\n"
"PO-Revision-Date: 2013-01-13 11:10+1300\n"
"Last-Translator: Rich <[email protected]>\n"
"Language-Team: French\n"
"Language: fr\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Plural-Forms: nplurals=2; plural=(n > 1);\n"

#: app/app.go:15
msgid "Yes."
msgstr "Oui."

Generate the binary (the file that'll actually get deployed with the app):

$ msgfmt -c -v -o locale/fr_FR/LC_MESSAGES/appname.mo french.po

Final directory structure:

~appname/
 |~app/
 | `-app.go
 |~github.com/
 | `~samuel/
 |   `~go-gettext/
 |     +locale/
 |     |-catalog.go
 |     |-domain.go
 |     `-mo.go
 |~locale/
 | `~fr_FR/
 |   `LC_MESSAGES/
 |    `-appname.mo 
 `-app.yaml

(locale directory under go-gettext holds test data, could be removed for deployment.)

If all goes well, a visit to appname should display "Oui."