Python i18n Modern

A modern internationalization (i18n) library for Python, inspired by i18n_modern for JavaScript.

Features

• 🌍 Simple and intuitive API for translations
• 📁 Support for multiple file formats: JSON, YAML, and TOML
• 🔄 Nested translation keys with dot notation
• 🎯 Conditional translations based on values
• 📝 Template string interpolation with [placeholder] syntax
• 💾 Built-in memoization for better performance
• 🔗 Deep object merging for locale inheritance
• ⚡ Flat locale structure for O(1) key lookups at runtime

Performance

Benchmarked against popular Python i18n libraries using pytest-benchmark on Linux and Windows (latest baseline: v0.2.3).

Operation	Resultado consistente
Simple key access	i18n_modern is fastest in both Linux and Windows
Nested key access	i18n_modern is fastest in both Linux and Windows
Parameter substitution	i18n_modern is fastest in both Linux and Windows
Conditional logic	Available in i18n_modern benchmark suite

Up to 580x faster than python-i18n on nested key access (Windows benchmark run).

For complete numbers, environment details, and per-library ranking, see BENCHMARK_REPORT.md.

Installation

# Basic installation (JSON support only)
pip install i18n_modern

# With YAML support
pip install i18n_modern[yaml]

# With TOML support (Python < 3.11)
pip install i18n_modern[toml]

# With all formats
pip install i18n_modern[all]

Quick Start

Loading from Dictionary

from i18n_modern import I18nModern

locales = {
    "greeting": "Hello, [name]!",
    "items": {
        "0": "No items",
        "1": "One item",
        "default": "[count] items"
    }
}

i18n = I18nModern("en", locales)
print(i18n.get("greeting", values={"name": "World"}))  # Hello, World!

Loading from Files

from i18n_modern import I18nModern

# Load from JSON
i18n = I18nModern("en", "locales/en.json")

# Load from YAML
i18n = I18nModern("es", "locales/es.yaml")

# Load from TOML
i18n = I18nModern("fr", "locales/fr.toml")

Example Files

locales/en.json

{
    "welcome": "Welcome to our app!",
    "greeting": "Hello, [name]!",
    "messages": {
        "success": "Operation successful",
        "error": "An error occurred"
    },
    "items": {
        "0": "No items",
        "1": "One item",
        "default": "[count] items"
    }
}

locales/es.yaml

welcome: "¡Bienvenido a nuestra aplicación!"
greeting: "¡Hola, [name]!"
messages:
  success: "Operación exitosa"
  error: "Ocurrió un error"
items:
  "0": "Sin elementos"
  "1": "Un elemento"
  default: "[count] elementos"

locales/fr.toml

welcome = "Bienvenue dans notre application!"
greeting = "Bonjour, [name]!"

[messages]
success = "Opération réussie"
error = "Une erreur s'est produite"

[items]
"0" = "Aucun élément"
"1" = "Un élément"
default = "[count] éléments"

Usage

Basic Translation

i18n = I18nModern("en", locales)
translation = i18n.get("welcome")

Nested Keys

translation = i18n.get("messages.success")

Template Interpolation

translation = i18n.get("greeting", values={"name": "Alice"})
# Output: Hello, Alice!

Conditional Translations

# Using exact matches
print(i18n.get("items", values={"count": 0}))  # No items
print(i18n.get("items", values={"count": 1}))  # One item
print(i18n.get("items", values={"count": 5}))  # 5 items

# Using comparisons
locales = {
    "age_group": {
        "[age] < 18": "Minor",
        "[age] >= 18": "Adult",
        "default": "Unknown"
    }
}

i18n = I18nModern("en", locales)
print(i18n.get("age_group", values={"age": 15}))  # Minor
print(i18n.get("age_group", values={"age": 25}))  # Adult

Multiple Locales

i18n = I18nModern("en")
i18n.load_from_file("locales/en.json", "en")
i18n.load_from_file("locales/es.json", "es")

# Use default locale (en)
print(i18n.get("greeting", values={"name": "World"}))

# Use specific locale
print(i18n.get("greeting", locale="es", values={"name": "Mundo"}))

Loading from Directory

You can load all translation files from a directory at once. This is useful when you have multiple files for a single locale.

# Structure:
# locales/
# ├── es_MX/
# │   ├── auth.yml
# │   ├── common.yml
# │   ├── document.yml
# │   └── roles.yml

i18n = I18nModern("es_MX")

# Load all files from directory - they will be merged together
# The directory name (es_MX) is used as the locale identifier
i18n.load_from_directory("locales/es_MX")

# Or specify a custom locale identifier
i18n.load_from_directory("locales/es_MX", locale_identify="spanish_mexico")

# Use filename as namespace for this specific call
i18n.load_from_directory("locales/es_MX", use_filename_as_namespace=True)

# Now you can access all translations
print(i18n.get("auth.login"))      # From auth.yml
print(i18n.get("common.welcome"))  # From common.yml
print(i18n.get("document.create")) # From document.yml

You can also enable this behavior at instance level:

i18n = I18nModern("es_MX", use_filename_as_namespace=True)
i18n.load_from_directory("locales/es_MX")

# Or toggle it later
i18n.use_filename_as_namespace = True

Changing Default Locale

i18n.default_locale = "es"
translation = i18n.get("welcome")  # Now uses Spanish

API Reference

I18nModern(default_locale, locales=None, use_filename_as_namespace=False)

Constructor for the i18n instance.

• default_locale (str): The default locale identifier
• locales (dict or str, optional): Initial locales dictionary or path to locale file
• use_filename_as_namespace (bool, optional): Default behavior for directory imports. When True, each file is namespaced by filename stem (for example, common.yml -> common.*)

get(key, locale=None, values=None)

Get a translation.

• key (str): Translation key (supports dot notation)
• locale (str, optional): Locale override
• values (dict, optional): Values for placeholder replacement
• Returns: Translated string

load_from_file(file_path, locale_identify)

Load translations from a file.

• file_path (str): Path to JSON, YAML, or TOML file
• locale_identify (str): Locale identifier

load_from_directory(directory_path, locale_identify=None, use_filename_as_namespace=None)

Load all translation files from a directory concurrently.

• directory_path (str): Path to directory containing locale files (JSON, YAML, TOML)
• locale_identify (str, optional): Locale identifier. If None, uses the directory name
• use_filename_as_namespace (bool, optional): Per-call override. If True, wraps every file under its filename stem; if None, uses the instance setting
• All files in the directory are merged together into a single locale entry

Supported file formats in directory: .json, .yaml, .yml, .toml

Example:

i18n = I18nModern("es_MX")
# Loads all .json, .yaml, .yml, and .toml files from the directory
i18n.load_from_directory("locales/es_MX")

# With custom locale identifier
i18n.load_from_directory("locales/es_MX", locale_identify="spanish")

# With per-call namespace override
i18n.load_from_directory("locales/es_MX", use_filename_as_namespace=True)

load_from_value(locales, locale_identify)

Load translations from a dictionary.

• locales (dict): Translations dictionary
• locale_identify (str): Locale identifier

Properties

• default_locale: Get or set the default locale
• use_filename_as_namespace: Get or set filename namespacing behavior for directory imports

License

MIT

Credits

Inspired by i18n_modern for JavaScript.