【Django】多言語化(i18n)完全実装ガイド｜gettext_lazy・makemessages・言語切り替えメニューまで

MIDDLEWARE = [
    'django.middleware.security.SecurityMiddleware',
    'django.contrib.sessions.middleware.SessionMiddleware',
    'django.middleware.locale.LocaleMiddleware',  # 追加
    'django.middleware.common.CommonMiddleware',
    'django.middleware.csrf.CsrfViewMiddleware',
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'django.contrib.messages.middleware.MessageMiddleware',
    'django.middleware.clickjacking.XFrameOptionsMiddleware',
]

LANGUAGE_CODE = 'ja'

USE_I18N = True   # 翻訳機能を有効化

from django.utils.translation import gettext_lazy as _

LANGUAGES = [
    ('en', _('English')),
    ('ja', _('Japanese')),
]

import os

LOCALE_PATHS = [os.path.join(BASE_DIR, 'locale')]

from django.contrib import admin
from django.urls import path, include
from django.conf.urls.i18n import i18n_patterns


urlpatterns = i18n_patterns(
    path('admin/', admin.site.urls),
    path('kakeibo/', include('kakeibo.urls')),
    prefix_default_language=False,
)

from django.db import models
from datetime import datetime
from django.utils.translation import gettext_lazy as _


class Category(models.Model):
    class Meta:
        verbose_name = _('category')
        verbose_name_plural = _('category')

    category_name = models.CharField(max_length=255, unique=True)

    def __str__(self):
        return self.category_name


class Kakeibo(models.Model):
    class Meta:
        verbose_name = _("Household account book")
        verbose_name_plural = _("Household account book")

    date = models.DateField(_("date"), default=datetime.now)
    category = models.ForeignKey(Category, on_delete=models.PROTECT, verbose_name=_("category"))
    money = models.IntegerField(_("Amount of money"), help_text=_("The unit is Japanese yen"))
    quantity = models.IntegerField(verbose_name=_("quantity"), default=0)
    memo = models.CharField(verbose_name=_("memo"), max_length=500)

    def __str__(self):
        return self.memo

from django.http import HttpResponse
from django.utils.translation import gettext as _


def my_view(request):
    output = _("ようこそホームページへ")
    return HttpResponse(output)

{% load i18n %}

<th class="text-center">{% trans "date" %}</th>
<th class="text-center">{% trans "category" %}</th>
<th class="text-center">{% trans "Amount of money" %}</th>
<th class="text-center">{% trans "quantity" %}</th>
<th class="text-center">{% trans "total fee" %}</th>
<th class="text-center">{% trans "memo" %}</th>
<th class="text-center">{% trans "Update / Delete" %}</th>

python manage.py makemessages -l ja

msgid "category"
msgstr "カテゴリ"

msgid "Household account book"
msgstr "家計簿アプリ"

msgid "date"
msgstr "日付"

msgid "Amount of money"
msgstr "金額"

msgid "The unit is Japanese yen"
msgstr "単位は日本円"

msgid "quantity"
msgstr "数量"

msgid "memo"
msgstr "メモ"

msgid "total fee"
msgstr "合計金額"

msgid "Update / Delete"
msgstr "更新/削除"

msgid "English"
msgstr "英語"

msgid "Japanese"
msgstr "日本語"

python manage.py compilemessages

from django import template
from django.template.defaultfilters import stringfilter
from django.conf import settings


def switch_lang_code(path, language):
    lang_codes = 

    if path == '':
        raise Exception('URL path for language switch is empty')
    elif path[0] != '/':
        raise Exception('URL path for language switch does not start with "/"')
    elif language not in lang_codes:
        raise Exception(f'{language} is not a supported language code')

    parts = path.split('/')

    if parts[1] in lang_codes:
        parts[1] = language
    else:
        parts[0] = "/" + language

    return '/'.join(parts)


register = template.Library()


@register.filter
@stringfilter
def switch_i18n_prefix(path, language):
    return switch_lang_code(path, language)


@register.filter
def switch_i18n(request, language):
    return switch_lang_code(request.get_full_path(), language)

{% extends "admin/base_site.html" %}
{% load i18n %}
{% load static %}
{% load i18n_switcher %}

{% block extrahead %}
    <link rel="shortcut icon" href="{% static 'images/favicon.ico' %}" />
    <link rel="stylesheet" type="text/css" href="{% static 'css/custom_admin.css' %}"/>
{% endblock %}

{% block userlinks %}
    <a href="{{ request|switch_i18n:'en' }}">
        <img class="i18n_flag" src="{% static 'images/flag-usa-16.png' %}"/>
    </a> /
    <a href="{{ request|switch_i18n:'ja' }}">
        <img class="i18n_flag" src="{% static 'images/flag-ja-16.png' %}"/>
    </a> /
    {% if user.is_active and user.is_staff %}
        {% url 'django-admindocs-docroot' as docsroot %}
        {% if docsroot %}
            <a href="{{ docsroot }}">{% trans 'Documentation' %}</a> /
        {% endif %}
    {% endif %}
    {% if user.has_usable_password %}
        <a href="{% url 'admin:password_change' %}">{% trans 'Change password' %}</a> /
    {% endif %}
    <a href="{% url 'admin:logout' %}">{% trans 'Log out' %}</a>
{% endblock %}

.i18n_flag img {
    width: 16px;
    vertical-align: text-top;
}

from django.urls import path, include
from django.conf.urls.i18n import i18n_patterns

urlpatterns = [
    path('i18n/', include('django.conf.urls.i18n')),  # 言語切り替え用エンドポイント
]

urlpatterns += i18n_patterns(
    path('admin/', admin.site.urls),
    path('kakeibo/', include('kakeibo.urls')),
    prefix_default_language=False,
)

<div class="btn-group float-right">
    <form action="{% url 'set_language' %}" method="post">{% csrf_token %}
        <input name="next" type="hidden" value="{{ redirect_to }}">
        <select name="language">
            {% get_current_language as LANGUAGE_CODE %}
            {% get_available_languages as LANGUAGES %}
            {% get_language_info_list for LANGUAGES as languages %}
            {% for language in languages %}
                <option value="{{ language.code }}"
                    {% if language.code == LANGUAGE_CODE %} selected{% endif %}>
                    {{ language.name_local }} ({{ language.code }})
                </option>
            {% endfor %}
        </select>
        <input type="submit" value="Go">
    </form>
</div>