Chapter 13: I18n and L10n (v0.13)

app/__init__.py

@@ -1,13 +1,14 @@
 import logging
 from logging.handlers import SMTPHandler, RotatingFileHandler
 import os
-from flask import Flask
+from flask import Flask, request
 from flask_sqlalchemy import SQLAlchemy
 from flask_migrate import Migrate
 from flask_login import LoginManager
 from flask_mail import Mail
 from flask_bootstrap import Bootstrap
 from flask_moment import Moment
+from flask_babel import Babel, lazy_gettext as _l
 from config import Config
 
 app = Flask(__name__)
@@ -16,9 +17,11 @@
 migrate = Migrate(app, db)
 login = LoginManager(app)
 login.login_view = 'login'
+login.login_message = _l('Please log in to access this page.')
 mail = Mail(app)
 bootstrap = Bootstrap(app)
 moment = Moment(app)
+babel = Babel(app)
 
 if not app.debug:
     if app.config['MAIL_SERVER']:
@@ -48,4 +51,10 @@
     app.logger.setLevel(logging.INFO)
     app.logger.info('Microblog startup')
 
+
+@babel.localeselector
+def get_locale():
+    return request.accept_languages.best_match(app.config['LANGUAGES'])
+
+
 from app import routes, models, errors

app/cli.py

@@ -0,0 +1,38 @@
+import os
+import click
+from app import app
+
+
+@app.cli.group()
+def translate():
+    """Translation and localization commands."""
+    pass
+
+
+@translate.command()
+@click.argument('lang')
+def init(lang):
+    """Initialize a new language."""
+    if os.system('pybabel extract -F babel.cfg -k _l -o messages.pot .'):
+        raise RuntimeError('extract command failed')
+    if os.system(
+            'pybabel init -i messages.pot -d app/translations -l ' + lang):
+        raise RuntimeError('init command failed')
+    os.remove('messages.pot')
+
+
+@translate.command()
+def update():
+    """Update all languages."""
+    if os.system('pybabel extract -F babel.cfg -k _l -o messages.pot .'):
+        raise RuntimeError('extract command failed')
+    if os.system('pybabel update -i messages.pot -d app/translations'):
+        raise RuntimeError('update command failed')
+    os.remove('messages.pot')
+
+
+@translate.command()
+def compile():
+    """Compile all languages."""
+    if os.system('pybabel compile -d app/translations'):
+        raise RuntimeError('compile command failed')

app/email.py

@@ -1,6 +1,7 @@
 from threading import Thread
 from flask import render_template
 from flask_mail import Message
+from flask_babel import _
 from app import app, mail
 
 
@@ -18,7 +19,7 @@ def send_email(subject, sender, recipients, text_body, html_body):
 
 def send_password_reset_email(user):
     token = user.get_reset_password_token()
-    send_email('[Microblog] Reset Your Password',
+    send_email(_('[Microblog] Reset Your Password'),
                sender=app.config['ADMINS'][0],
                recipients=[user.email],
                text_body=render_template('email/reset_password.txt',

app/forms.py

@@ -3,51 +3,55 @@
     TextAreaField
 from wtforms.validators import ValidationError, DataRequired, Email, EqualTo, \
     Length
+from flask_babel import _, lazy_gettext as _l
 from app.models import User
 
 
 class LoginForm(FlaskForm):
-    username = StringField('Username', validators=[DataRequired()])
-    password = PasswordField('Password', validators=[DataRequired()])
-    remember_me = BooleanField('Remember Me')
-    submit = SubmitField('Sign In')
+    username = StringField(_l('Username'), validators=[DataRequired()])
+    password = PasswordField(_l('Password'), validators=[DataRequired()])
+    remember_me = BooleanField(_l('Remember Me'))
+    submit = SubmitField(_l('Sign In'))
 
 
 class RegistrationForm(FlaskForm):
-    username = StringField('Username', validators=[DataRequired()])
-    email = StringField('Email', validators=[DataRequired(), Email()])
-    password = PasswordField('Password', validators=[DataRequired()])
+    username = StringField(_l('Username'), validators=[DataRequired()])
+    email = StringField(_l('Email'), validators=[DataRequired(), Email()])
+    password = PasswordField(_l('Password'), validators=[DataRequired()])
     password2 = PasswordField(
-        'Repeat Password', validators=[DataRequired(), EqualTo('password')])
-    submit = SubmitField('Register')
+        _l('Repeat Password'), validators=[DataRequired(),
+                                           EqualTo('password')])
+    submit = SubmitField(_l('Register'))
 
     def validate_username(self, username):
         user = User.query.filter_by(username=username.data).first()
         if user is not None:
-            raise ValidationError('Please use a different username.')
+            raise ValidationError(_('Please use a different username.'))
 
     def validate_email(self, email):
         user = User.query.filter_by(email=email.data).first()
         if user is not None:
-            raise ValidationError('Please use a different email address.')
+            raise ValidationError(_('Please use a different email address.'))
 
 
 class ResetPasswordRequestForm(FlaskForm):
-    email = StringField('Email', validators=[DataRequired(), Email()])
-    submit = SubmitField('Request Password Reset')
+    email = StringField(_l('Email'), validators=[DataRequired(), Email()])
+    submit = SubmitField(_l('Request Password Reset'))
 
 
 class ResetPasswordForm(FlaskForm):
-    password = PasswordField('Password', validators=[DataRequired()])
+    password = PasswordField(_l('Password'), validators=[DataRequired()])
     password2 = PasswordField(
-        'Repeat Password', validators=[DataRequired(), EqualTo('password')])
-    submit = SubmitField('Request Password Reset')
+        _l('Repeat Password'), validators=[DataRequired(),
+                                           EqualTo('password')])
+    submit = SubmitField(_l('Request Password Reset'))
 
 
 class EditProfileForm(FlaskForm):
-    username = StringField('Username', validators=[DataRequired()])
-    about_me = TextAreaField('About me', validators=[Length(min=0, max=140)])
-    submit = SubmitField('Submit')
+    username = StringField(_l('Username'), validators=[DataRequired()])
+    about_me = TextAreaField(_l('About me'),
+                             validators=[Length(min=0, max=140)])
+    submit = SubmitField(_l('Submit'))
 
     def __init__(self, original_username, *args, **kwargs):
         super(EditProfileForm, self).__init__(*args, **kwargs)
@@ -57,13 +61,13 @@ def validate_username(self, username):
         if username.data != self.original_username:
             user = User.query.filter_by(username=self.username.data).first()
             if user is not None:
-                raise ValidationError('Please use a different username.')
+                raise ValidationError(_('Please use a different username.'))
 
 
 class EmptyForm(FlaskForm):
     submit = SubmitField('Submit')
 
 
 class PostForm(FlaskForm):
-    post = TextAreaField('Say something', validators=[DataRequired()])
-    submit = SubmitField('Submit')
+    post = TextAreaField(_l('Say something'), validators=[DataRequired()])
+    submit = SubmitField(_l('Submit'))

app/routes.py

@@ -1,7 +1,8 @@
 from datetime import datetime
-from flask import render_template, flash, redirect, url_for, request
+from flask import render_template, flash, redirect, url_for, request, g
 from flask_login import login_user, logout_user, current_user, login_required
 from werkzeug.urls import url_parse
+from flask_babel import _, get_locale
 from app import app, db
 from app.forms import LoginForm, RegistrationForm, EditProfileForm, \
     EmptyForm, PostForm, ResetPasswordRequestForm, ResetPasswordForm
@@ -14,6 +15,7 @@ def before_request():
     if current_user.is_authenticated:
         current_user.last_seen = datetime.utcnow()
         db.session.commit()
+    g.locale = str(get_locale())
 
 
 @app.route('/', methods=['GET', 'POST'])
@@ -25,7 +27,7 @@ def index():
         post = Post(body=form.post.data, author=current_user)
         db.session.add(post)
         db.session.commit()
-        flash('Your post is now live!')
+        flash(_('Your post is now live!'))
         return redirect(url_for('index'))
     page = request.args.get('page', 1, type=int)
     posts = current_user.followed_posts().paginate(
@@ -34,7 +36,7 @@ def index():
         if posts.has_next else None
     prev_url = url_for('index', page=posts.prev_num) \
         if posts.has_prev else None
-    return render_template('index.html', title='Home', form=form,
+    return render_template('index.html', title=_('Home'), form=form,
                            posts=posts.items, next_url=next_url,
                            prev_url=prev_url)
 
@@ -49,8 +51,9 @@ def explore():
         if posts.has_next else None
     prev_url = url_for('explore', page=posts.prev_num) \
         if posts.has_prev else None
-    return render_template('index.html', title='Explore', posts=posts.items,
-                           next_url=next_url, prev_url=prev_url)
+    return render_template('index.html', title=_('Explore'),
+                           posts=posts.items, next_url=next_url,
+                           prev_url=prev_url)
 
 
 @app.route('/login', methods=['GET', 'POST'])
@@ -61,14 +64,14 @@ def login():
     if form.validate_on_submit():
         user = User.query.filter_by(username=form.username.data).first()
         if user is None or not user.check_password(form.password.data):
-            flash('Invalid username or password')
+            flash(_('Invalid username or password'))
             return redirect(url_for('login'))
         login_user(user, remember=form.remember_me.data)
         next_page = request.args.get('next')
         if not next_page or url_parse(next_page).netloc != '':
             next_page = url_for('index')
         return redirect(next_page)
-    return render_template('login.html', title='Sign In', form=form)
+    return render_template('login.html', title=_('Sign In'), form=form)
 
 
 @app.route('/logout')
@@ -87,9 +90,9 @@ def register():
         user.set_password(form.password.data)
         db.session.add(user)
         db.session.commit()
-        flash('Congratulations, you are now a registered user!')
+        flash(_('Congratulations, you are now a registered user!'))
         return redirect(url_for('login'))
-    return render_template('register.html', title='Register', form=form)
+    return render_template('register.html', title=_('Register'), form=form)
 
 
 @app.route('/reset_password_request', methods=['GET', 'POST'])
@@ -101,10 +104,11 @@ def reset_password_request():
         user = User.query.filter_by(email=form.email.data).first()
         if user:
             send_password_reset_email(user)
-        flash('Check your email for the instructions to reset your password')
+        flash(
+            _('Check your email for the instructions to reset your password'))
         return redirect(url_for('login'))
     return render_template('reset_password_request.html',
-                           title='Reset Password', form=form)
+                           title=_('Reset Password'), form=form)
 
 
 @app.route('/reset_password/<token>', methods=['GET', 'POST'])
@@ -118,7 +122,7 @@ def reset_password(token):
     if form.validate_on_submit():
         user.set_password(form.password.data)
         db.session.commit()
-        flash('Your password has been reset.')
+        flash(_('Your password has been reset.'))
         return redirect(url_for('login'))
     return render_template('reset_password.html', form=form)
 
@@ -147,12 +151,12 @@ def edit_profile():
         current_user.username = form.username.data
         current_user.about_me = form.about_me.data
         db.session.commit()
-        flash('Your changes have been saved.')
+        flash(_('Your changes have been saved.'))
         return redirect(url_for('edit_profile'))
     elif request.method == 'GET':
         form.username.data = current_user.username
         form.about_me.data = current_user.about_me
-    return render_template('edit_profile.html', title='Edit Profile',
+    return render_template('edit_profile.html', title=_('Edit Profile'),
                            form=form)
 
 
@@ -163,14 +167,14 @@ def follow(username):
     if form.validate_on_submit():
         user = User.query.filter_by(username=username).first()
         if user is None:
-            flash('User {} not found.'.format(username))
+            flash(_('User %(username)s not found.', username=username))
             return redirect(url_for('index'))
         if user == current_user:
-            flash('You cannot follow yourself!')
+            flash(_('You cannot follow yourself!'))
             return redirect(url_for('user', username=username))
         current_user.follow(user)
         db.session.commit()
-        flash('You are following {}!'.format(username))
+        flash(_('You are following %(username)s!', username=username))
         return redirect(url_for('user', username=username))
     else:
         return redirect(url_for('index'))
@@ -183,14 +187,14 @@ def unfollow(username):
     if form.validate_on_submit():
         user = User.query.filter_by(username=username).first()
         if user is None:
-            flash('User {} not found.'.format(username))
+            flash(_('User %(username)s not found.', username=username))
             return redirect(url_for('index'))
         if user == current_user:
-            flash('You cannot unfollow yourself!')
+            flash(_('You cannot unfollow yourself!'))
             return redirect(url_for('user', username=username))
         current_user.unfollow(user)
         db.session.commit()
-        flash('You are not following {}.'.format(username))
+        flash(_('You are not following %(username)s.', username=username))
         return redirect(url_for('user', username=username))
     else:
         return redirect(url_for('index'))

app/templates/404.html

@@ -1,6 +1,6 @@
 {% extends "base.html" %}
 
 {% block app_content %}
-    <h1>Not Found</h1>
-    <p><a href="{{ url_for('index') }}">Back</a></p>
+    <h1>{{ _('Not Found') }}</h1>
+    <p><a href="{{ url_for('index') }}">{{ _('Back') }}</a></p>
 {% endblock %}

app/templates/500.html

@@ -1,7 +1,7 @@
 {% extends "base.html" %}
 
 {% block app_content %}
-    <h1>An unexpected error has occurred</h1>
-    <p>The administrator has been notified. Sorry for the inconvenience!</p>
-    <p><a href="{{ url_for('index') }}">Back</a></p>
+    <h1>{{ _('An unexpected error has occurred') }}</h1>
+    <p>{{ _('The administrator has been notified. Sorry for the inconvenience!') }}</p>
+    <p><a href="{{ url_for('index') }}">{{ _('Back') }}</a></p>
 {% endblock %}

app/templates/_post.html

@@ -6,10 +6,13 @@
                 </a>
             </td>
             <td>
-                <a href="{{ url_for('user', username=post.author.username) }}">
-                    {{ post.author.username }}
-                </a>
-                said {{ moment(post.timestamp).fromNow() }}:
+                {% set user_link %}
+                    <a href="{{ url_for('user', username=post.author.username) }}">
+                        {{ post.author.username }}
+                    </a>
+                {% endset %}
+                {{ _('%(username)s said %(when)s',
+                    username=user_link, when=moment(post.timestamp).fromNow()) }}
                 <br>
                 {{ post.body }}
             </td>