Lib.rs

banana-i18n

A Rust library for internationalization (i18n) with MediaWiki-style message formatting and localization.

Overview

banana-i18n-rust is a robust i18n library designed to handle complex multilingual message formatting with support for:

• PLURAL magic words - Automatic plural form selection based on ICU plural rules supporting 56+ languages
• GENDER magic words - Gender-based form selection (masculine, feminine, neutral)
• Placeholder substitution - Support for numbered placeholders ($1, $2, etc.)
• Wiki links - Parsing and handling of wiki markup links
• External links - Support for URLs and hyperlinks
• Locale fallback chains - Automatic fallback from specific locales to more general ones (e.g., de-at → de → en)
• Verbosity-controlled logging - Three levels of logging for debugging localization chains

Features

PLURAL Magic Word

Selects the correct plural form based on a number and language rules. Uses ICU CLDR plural rules for accurate localization across different languages.

Format: {{PLURAL:value|singular|plural}}

Supported forms (per language):

• English: 2 forms (one, other)
• Russian: 3 forms (one, few, many)
• Polish: 3 forms
• Arabic: 6 forms
• French: 2 forms with special rules
• Chinese: 1 form (no plural distinction)
• 56+ languages supported via ICU plural rules

Examples:

{{PLURAL:$1|There is|There are}} $1 item
→ "There is 1 item" (with value=1)
→ "There are 5 items" (with value=5)

В коробке находится {{PLURAL:$1|предмет|предметов}}
→ "В коробке находится предмет" (Russian, value=1)
→ "В коробке находится предметов" (Russian, value=5)

GENDER Magic Word

Selects the correct form based on gender (male, female, neutral).

Format: {{GENDER:value|masculine|feminine|neutral}}

Examples:

{{GENDER:$1|He|She|They}} is here
→ "He is here" (with gender=male)
→ "She is here" (with gender=female)
→ "They is here" (with gender=other)

Placeholder Substitution

Replace numbered placeholders with provided values.

Format: $1, $2, $3, etc.

Examples:

Hello, $1!
→ "Hello, World!" (with $1=World)

$1 sent a message to $2
→ "Alice sent a message to Bob" (with $1=Alice, $2=Bob)

Locale Fallback Chains

Automatically fall back from specific locales to more general ones:

• de-at → de → en (German Austria → German → English)
• zh-hans → zh → en (Simplified Chinese → Chinese → English)
• fr-ca → fr → en (Canadian French → French → English)

Messages are loaded from the first available locale in the fallback chain.

Installation

As a Library

Add to your Cargo.toml:

[dependencies]
banana-i18n = { path = "." }  # or from crates.io when published
serde_json = "1.0"

From Source

git clone <repository>
cd banana-i18n-rust
cargo build --release

Usage

CLI Tool

The library includes a command-line tool for testing and using localized messages.

Basic Usage

# Build the binary
cargo build --release

# Display help
./target/release/banana-i18n

# Localize a message
./target/release/banana-i18n <locale> <message-key> [param1] [param2] ...

Examples

# Simple message with substitution
./target/release/banana-i18n en greeting "World"
# Output: Hello, World!

# Plural forms
./target/release/banana-i18n en plural "1"
# Output: There is 1 item in the box

./target/release/banana-i18n en plural "5"
# Output: There are 5 items in the box

# Gender-based forms
./target/release/banana-i18n en pronoun "male"
# Output: He is here

./target/release/banana-i18n en pronoun "female"
# Output: She is here

# Russian (3-form plurals)
./target/release/banana-i18n ru items "1"
# Output: В коробке находится 1 предмет

./target/release/banana-i18n ru items "5"
# Output: В коробке находится 5 предметов

# Locale fallback
./target/release/banana-i18n de-at greeting "Wien"
# Output: Guten Tag, Wien! (falls back from de-at → de)

# Chinese
./target/release/banana-i18n zh-hans greeting "北京"
# Output: 你好，北京

Environment Variables

Override the default messages directory:

I18N_MESSAGES_DIR=/path/to/messages ./target/release/banana-i18n en greeting "World"

Using as a Library

use banana_i18n::{I18n, loader};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Load messages from directory
    let mut i18n = I18n::new();
    i18n.load_all_locales("i18n")?;

    // Get a message with locale fallback
    let message = i18n.get_message("en", "greeting");
    println!("{}", message); // "Hello, World!" or key name

    Ok(())
}

Message Format

Messages are stored in JSON files with locale codes as filenames:

File: en.json

{
  "@metadata": {
    "authors": ["Your Name"],
    "description": "English messages"
  },
  "greeting": "Hello, $1!",
  "plural": "There {{PLURAL:$1|is|are}} $1 item in the box",
  "pronoun": "{{GENDER:$1|He|She|They}} is here"
}

File: ru.json

{
  "@metadata": {
    "authors": ["Ваше имя"],
    "description": "Russian messages"
  },
  "greeting": "Привет, $1!",
  "items": "В коробке находится {{PLURAL:$1|предмет|предметов|предметов}}"
}

JSON Format Specification

• @metadata (optional): Document metadata (skipped during parsing)

  • authors: List of translators
  • description: Description of message set
  • Other custom metadata fields are ignored

• Message keys (required): Message strings with MediaWiki format

  • Supports all magic words (PLURAL, GENDER)
  • Supports placeholders ($1, $2, etc.)
  • Supports wiki links ([[link]], [[link|display]])
  • Supports external links (http://url, http://url text)

Core Components

• I18n struct: Main entry point managing localized messages by locale
• LocalizedMessages: Wrapper around HashMap for key-value message pairs
• AstNode enum: Represents different types of wiki markup:
  • Placeholder - Numbered variables ($1, $2)
  • Text - Plain text content
  • InternalLink - Wiki links [[page]] or [[page|text]]
  • ExternalLink - URLs http://example.com text
  • Gender - GENDER magic word
  • Plural - PLURAL magic word
• Parser: Converts MediaWiki message format strings into AST nodes
• Localizer: Applies value substitution and performs localization

Localization Flow

1. Parse - Convert message string to AST using wikitext parser
2. Localize - Traverse AST and apply substitutions
   • Replace placeholders with provided values
   • Evaluate PLURAL forms based on language rules
   • Evaluate GENDER forms based on provided gender
3. Fallback - If message not found, try fallback locale chain

License

MIT License - See LICENSE file for details

References

• MediaWiki Message Format Documentation
• ICU CLDR Plural Rules
• ISO 639-1 Language Codes