Android アプリのローカリゼーション完全ガイド

// Android project structure for localization:
// res/
// ├── values/              ← Default (fallback) locale
// │   └── strings.xml
// ├── values-de/           ← German
// │   └── strings.xml
// ├── values-ja/           ← Japanese
// │   └── strings.xml
// └── values-es/           ← Spanish
//     └── strings.xml
//
// Folder naming: values-{language} or values-{language}-r{Region}
// Examples: values-pt-rBR, values-zh-rCN, values-zh-rTW

<!-- res/values/strings.xml -->
<resources>
    <string name="welcome_title">Welcome to MyApp</string>
    <string name="login_button">Sign In</string>
    <string name="settings_label">Settings</string>
    <string name="greeting">Hello, %s!</string>        <!-- %s = string -->
    <string name="item_count">%d items</string>          <!-- %d = integer -->
    <string name="app_name" translatable="false">MyApp</string>
</resources>

<!-- ❌ Common mistakes in strings.xml: -->

<!-- Unescaped apostrophe — crashes XML parser silently -->
<string name="message">It's a great day</string>

<!-- Missing from default values/strings.xml — app crashes -->
<!-- (only exists in values-de/strings.xml) -->

<!-- ✅ Correct versions: -->
<string name="message">It\'s a great day</string>
<!-- Or wrap in double quotes: -->
<string name="message">"It's a great day"</string>

<!-- res/values/strings.xml -->
<resources>
    <plurals name="items_count">
        <item quantity="zero">No items</item>
        <item quantity="one">%d item</item>
        <item quantity="other">%d items</item>
    </plurals>
</resources>

<!-- Usage in Kotlin: -->
<!-- val text = resources.getQuantityString(
    R.plurals.items_count,
    count,    // selects plural form
    count     // format argument
) -->

// Traditional Android (Activity/Fragment)
val title = getString(R.string.welcome_title)
val greeting = getString(R.string.greeting, userName)
val items = resources.getQuantityString(
    R.plurals.items_count, count, count
)

// Jetpack Compose
@Composable
fun WelcomeScreen(userName: String, itemCount: Int) {
    // ✅ stringResource — Compose-aware, triggers recomposition
    Text(text = stringResource(R.string.welcome_title))

    // ✅ With format arguments
    Text(text = stringResource(R.string.greeting, userName))

    // ✅ Plurals — count passed TWICE
    Text(text = pluralStringResource(
        R.plurals.items_count,
        itemCount,    // selects plural form
        itemCount     // format argument
    ))
}

<!-- res/values/strings.xml -->
<resources>
    <!-- String array for dropdown/list -->
    <string-array name="sort_options">
        <item>Most Recent</item>
        <item>Most Popular</item>
        <item>Price: Low to High</item>
        <item>Price: High to Low</item>
    </string-array>

    <!-- Positional format args for reordering -->
    <string name="welcome_message">
        Hello %1$s, you have %2$d new messages
    </string>
    <!-- Translators can reorder: -->
    <!-- %2$d neue Nachrichten für %1$s -->
</resources>

# Install Fastlane
$ gem install fastlane

# Initialize supply for Play Store metadata
$ fastlane supply init

# Directory structure created:
# fastlane/metadata/android/
# ├── en-US/
# │   ├── title.txt              # App name (50 chars)
# │   ├── short_description.txt  # Short desc (80 chars)
# │   ├── full_description.txt   # Full desc (4000 chars)
# │   └── changelogs/
# │       └── default.txt        # What's New
# ├── de-DE/
# │   └── ...
# └── ja-JP/
#     └── ...

# Push metadata to Play Store:
$ fastlane supply

// 1. Emulator: Settings > System > Language > Add language

// 2. Compose Preview with locale:
@Preview
@Composable
fun WelcomePreview() {
    val config = Configuration(resources.configuration).apply {
        setLocale(Locale("de"))
    }
    val localContext = LocalContext.current
    val localizedContext = localContext.createConfigurationContext(config)
    CompositionLocalProvider(
        LocalContext provides localizedContext
    ) {
        WelcomeScreen()
    }
}

// 3. Restrict library locales in build.gradle.kts:
android {
    defaultConfig {
        // Only include locales you actually translate
        resourceConfigurations += listOf("en", "de", "ja", "es", "fr")
    }
}

// 4. Enable pseudolocales in Developer Options:
// en-XA (accented) — detects hardcoded strings
// ar-XB (RTL) — tests layout mirroring

# Translate strings.xml files
> Translate res/values/strings.xml
  to Japanese, German, and Spanish

# Translate Play Store metadata too
> Translate fastlane/metadata/android/en-US/
  to de-DE, ja-JP, es-ES

✓ 6 files translated in 3.2s

MyApp/
├── app/
│   └── src/main/
│       ├── res/
│       │   ├── values/
│       │   │   ├── strings.xml          # Default (source) strings
│       │   │   └── plurals.xml          # Plural rules
│       │   ├── values-de/
│       │   │   └── strings.xml
│       │   ├── values-ja/
│       │   │   └── strings.xml
│       │   └── values-es/
│       │       └── strings.xml
│       ├── java/com/example/myapp/
│       └── AndroidManifest.xml
├── fastlane/
│   └── metadata/android/
│       ├── en-US/
│       │   ├── title.txt
│       │   ├── short_description.txt
│       │   ├── full_description.txt
│       │   └── changelogs/default.txt
│       ├── de-DE/
│       └── ja-JP/
├── build.gradle.kts
└── settings.gradle.kts