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# Flask-Babel
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Flask-Babel provides internationalization (i18n) and localization (l10n) support for Flask web applications. Built on top of Python Babel and pytz libraries, it enables developers to create multi-language Flask applications with utilities for message translation, date/time formatting, number formatting, and locale-aware content rendering.
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## Package Information
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- **Package Name**: flask-babel
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- **Language**: Python
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- **Installation**: `pip install flask-babel`
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## Core Imports
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```python
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from flask_babel import Babel, gettext, ngettext, format_datetime
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```
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Common pattern for Flask applications:
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```python
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from flask_babel import Babel
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from flask_babel import gettext as _, ngettext, lazy_gettext
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```
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## Basic Usage
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```python
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from flask import Flask
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from flask_babel import Babel, gettext, ngettext, get_locale
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app = Flask(__name__)
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app.config['BABEL_DEFAULT_LOCALE'] = 'en'
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app.config['BABEL_DEFAULT_TIMEZONE'] = 'UTC'
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babel = Babel(app)
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@babel.localeselector
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def get_locale():
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    return request.accept_languages.best_match(['en', 'es', 'fr'])
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@app.route('/')
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def index():
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    # Simple translation
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    message = gettext('Hello World!')
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    # Plural translation
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    count = 5
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    plural_message = ngettext(
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        '%(num)d item found',
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        '%(num)d items found',
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        count
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    )
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    # Date formatting
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    from datetime import datetime
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    from flask_babel import format_datetime
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    now = datetime.utcnow()
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    formatted_date = format_datetime(now, 'medium')
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    return f"{message}<br>{plural_message}<br>{formatted_date}"
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```
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## Architecture
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Flask-Babel integrates with Flask's application context and provides:
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- **Babel**: Main configuration class that initializes i18n support
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- **Domain**: Manages translation catalogs and message domains
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- **Context Integration**: Automatic locale detection and timezone handling via Flask's request context
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- **Lazy Evaluation**: LazyString objects for translations that resolve at render time
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- **Jinja2 Integration**: Automatic template filters and functions for formatting
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## Capabilities
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### Application Configuration
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Initialize and configure Flask-Babel for your Flask application with locale selectors, timezone handling, and translation directory management.
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```python { .api }
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class Babel:
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    def __init__(self, app=None, date_formats=None, configure_jinja=True, *args, **kwargs): ...
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    def init_app(self, app, default_locale='en', default_domain='messages', 
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                 default_translation_directories='translations', default_timezone='UTC',
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                 locale_selector=None, timezone_selector=None): ...
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    def list_translations(self): ...
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```
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[Configuration](./configuration.md)
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### Translation Functions
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Translate strings with support for pluralization, context, and lazy evaluation. Includes immediate and lazy translation functions for different use cases.
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```python { .api }
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def gettext(string, **variables): ...
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def ngettext(singular, plural, num, **variables): ...
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def pgettext(context, string, **variables): ...
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def lazy_gettext(string, **variables): ...
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def lazy_ngettext(singular, plural, num, **variables): ...
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```
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[Translation](./translation.md)
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### Date, Time, and Number Formatting
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Format dates, times, numbers, and currencies according to the current locale with support for custom formats and timezone conversion.
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```python { .api }
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def format_datetime(datetime=None, format=None, rebase=True): ...
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def format_date(date=None, format=None, rebase=True): ...
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def format_time(time=None, format=None, rebase=True): ...
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def format_currency(number, currency, format=None, currency_digits=True, format_type='standard'): ...
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def format_number(number): ...
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```
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[Formatting](./formatting.md)