Resources & Localization

Resources are Android's mechanism for adapting content to device configuration — locale, density, orientation, theme, API level. Done right, adding a new language is a text-file import; a new form factor is zero code. Done wrong, translations break, layouts clip, and users in RTL locales see garbage. This chapter covers the resource system end to end.

Resource qualifiers

Every resource folder under res/ can have qualifiers that narrow when it applies:

res/
├── values/                          default values
├── values-night/                    dark mode
├── values-es/                       Spanish
├── values-hi/                       Hindi
├── values-ar/                       Arabic
├── values-sw600dp/                  tablet portrait
├── values-w720dp/                   tablet landscape / large phone
├── values-land/                     landscape
├── values-v31/                      API 31+ (Android 12+)
├── layout/
├── layout-sw600dp/
├── drawable/
├── drawable-hdpi/ -mdpi/ -xhdpi/ -xxhdpi/ -xxxhdpi/
├── drawable-v24/                    vector drawables that need API 24+ features
├── mipmap-anydpi-v26/               adaptive launcher icons
├── raw/                             raw files (fonts, JSON, audio)
├── font/                            font resources
└── xml/                             arbitrary XML

Qualifiers stack: values-sw600dp-land-night/ applies on tablet, landscape, dark mode. Order matters in folder names — see the resource qualifier precedence table.

---

Strings

Basic strings

<!-- res/values/strings.xml -->
<resources>
    <string name="app_name">My App</string>
    <string name="greeting">Hello, %1$s!</string>
    <string name="items_selected">%1$d items selected</string>
</resources>

Accessing from code

val name = context.getString(R.string.greeting, user.name)

// In Compose
@Composable
fun Greeting(user: User) {
    Text(stringResource(R.string.greeting, user.name))
}

Format specifiers

Use numbered specifiers (%1$s, %2$d) not unnumbered (%s) — some languages need to reorder arguments:

<!-- English -->
<string name="duration">%1$d minutes and %2$d seconds</string>

<!-- Japanese reorders -->
<string name="duration">%2$d秒と%1$d分</string>

Without numbering, the reorder is impossible — translation breaks.

Plurals

<plurals name="item_count">
    <item quantity="zero">No items</item>
    <item quantity="one">1 item</item>
    <item quantity="other">%d items</item>
</plurals>

val text = context.resources.getQuantityString(R.plurals.item_count, count, count)

// Compose
Text(pluralStringResource(R.plurals.item_count, count, count))

Different languages have different plural rules — Arabic has six forms (zero, one, two, few, many, other), Chinese has one (other). Always use <plurals> for countable nouns, never string concatenation.

ICU MessageFormat (Android 7+)

For gendered or complex formatting, use ICU:

<string name="message_preview">
    {gender, select,
        female {She sent you a message}
        male {He sent you a message}
        other {They sent you a message}
    }
</string>

val text = context.getString(
    R.string.message_preview,
    mapOf("gender" to user.gender)
)

More powerful than Android's built-in format specifiers — handles gender, nested plurals, select variants.

---

Dates, numbers, currency

Use the system locale, not your custom formatters:

val locale = Locale.getDefault()

// Dates (java.time since API 26)
val formatter = DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM).withLocale(locale)
val text = formatter.format(LocalDate.now())
// en-US: "Jul 15, 2025"
// de-DE: "15. Juli 2025"
// ja-JP: "2025年7月15日"

// Numbers
val number = NumberFormat.getNumberInstance(locale).format(1_234_567.89)
// en-US: "1,234,567.89"
// de-DE: "1.234.567,89"
// fr-FR: "1 234 567,89"

// Currency
val currency = NumberFormat.getCurrencyInstance(locale).apply {
    currency = Currency.getInstance("USD")   // always specify — device locale might be EUR
}.format(99.95)
// en-US: "$99.95"
// de-DE: "99,95 $"

Hardcoded formatting like "$%.2f".format(price) breaks for non-English locales.

---

Dimensions and densities

<!-- res/values/dimens.xml -->
<resources>
    <dimen name="list_item_padding">16dp</dimen>
    <dimen name="title_text_size">18sp</dimen>
</resources>

<!-- res/values-sw600dp/dimens.xml — overrides for tablets -->
<resources>
    <dimen name="list_item_padding">24dp</dimen>
    <dimen name="title_text_size">22sp</dimen>
</resources>

dp scales with density; sp scales with density AND font size setting. Always use sp for text, dp for everything else.

In Compose:

val padding = dimensionResource(R.dimen.list_item_padding)

Text(
    text = "Title",
    fontSize = with(LocalDensity.current) { dimensionResource(R.dimen.title_text_size).toSp() }
)

---

Drawables

Vector drawables — scalable, tiny

<!-- res/drawable/ic_cart.xml -->
<vector xmlns:android="http://schemas.android.com/apk/res/android"
    android:width="24dp" android:height="24dp"
    android:viewportWidth="24" android:viewportHeight="24"
    android:tint="?attr/colorControlNormal">
    <path android:fillColor="@android:color/white"
        android:pathData="M7,18c-1.1,0 -1.99,0.9 -1.99,2 ..."/>
</vector>

Vectors replace 5+ PNG density buckets with one file. Use Android Studio's vector asset importer.

Tint and states

<!-- res/drawable/ic_favorite_state.xml -->
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_checked="true" android:drawable="@drawable/ic_favorite_filled"/>
    <item android:drawable="@drawable/ic_favorite_outlined"/>
</selector>

For Compose, do this with state directly — no selector XML needed.

Adaptive icons (API 26+)

<!-- res/mipmap-anydpi-v26/ic_launcher.xml -->
<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
    <background android:drawable="@drawable/ic_launcher_background"/>
    <foreground android:drawable="@drawable/ic_launcher_foreground"/>
    <monochrome android:drawable="@drawable/ic_launcher_monochrome"/>   <!-- for Material You themed icons -->
</adaptive-icon>

The OS masks the icon into the device's icon shape (circle, squircle, etc.) — one icon, consistent across OEMs.

---

Colors and themes

<!-- res/values/colors.xml — always define colors as resources -->
<resources>
    <color name="primary_green">#0F9D58</color>
    <color name="on_primary">#FFFFFF</color>
</resources>

<!-- res/values/themes.xml -->
<resources>
    <style name="Theme.MyApp" parent="Theme.Material3.DayNight.NoActionBar">
        <item name="colorPrimary">@color/primary_green</item>
        <item name="colorOnPrimary">@color/on_primary</item>
    </style>
</resources>

<!-- res/values-night/themes.xml — dark variants -->
<resources>
    <style name="Theme.MyApp" parent="Theme.Material3.DayNight.NoActionBar">
        <item name="colorPrimary">@color/primary_green_dark</item>
    </style>
</resources>

In Compose you mostly use MaterialTheme.colorScheme.*, not these. But non-Compose screens and system UI (notification color, splash) still need theme attributes.

---

Right-to-left (RTL)

Arabic, Hebrew, Persian, Urdu all use RTL scripts. Android flips the UI automatically if you:

1. Opt in

<!-- AndroidManifest.xml -->
<application android:supportsRtl="true">

2. Use start/end everywhere, never left/right

<!-- XML -->
<LinearLayout
    android:paddingStart="16dp"
    android:paddingEnd="8dp"
    android:layout_marginStart="8dp"/>

// Compose
Modifier.padding(start = 16.dp, end = 8.dp)
Row(horizontalArrangement = Arrangement.spacedBy(8.dp)) { /* ... */ }

3. Mirror directional icons

<!-- Arrow icons that have direction — mirror in RTL -->
<vector android:autoMirrored="true" .../>

// Compose — AutoMirrored variants
Icon(Icons.AutoMirrored.Filled.ArrowForward, contentDescription = null)

4. Test with pseudo-localization or real RTL locale

adb shell settings put system locale ar-EG
adb shell settings put system layout_direction 1     # force RTL

Or use locale-qualified resources:

<!-- res/values-ar/strings.xml -->
<resources>
    <string name="greeting">مرحبا، %1$s!</string>
</resources>

Android flips layouts automatically — your job is to avoid hardcoding direction.

---

Pseudo-localization

Before translating, wrap strings with pseudo-localization to catch RTL and length bugs:

adb shell setprop persist.sys.locale en-XA
adb shell stop; adb shell start

en-XA produces [!!!Hëllø, Wörld !!!] — readable but expanded ~30%. RTL variant is ar-XB — flipped text, forces layout to render right- to-left.

Android Studio → Help → Edit Custom Properties → add enable.pseudo.locales=true if not already.

Compose preview

@Preview(locale = "ar", showBackground = true)
@Preview(locale = "en-XA", showBackground = true)
@Composable
fun GreetingPreview() { /* ... */ }

Catches clipped layouts before any translation is written.

---

Translation workflow

Typical enterprise pipeline:

1. Developer writes strings.xml with English (default locale)
2. CI sends new strings to Translation Management System (TMS):
   - Lokalise, Phrase, Crowdin, Smartling
3. Translators produce strings-es.xml, strings-fr.xml, etc.
4. TMS pushes back → your repo
5. Lint verifies every string exists in every supported language

Mark strings not translatable

<string name="app_version" translatable="false">1.2.3</string>

Prevents sending internal identifiers to translators.

xliff:g for placeholders

<string name="greeting">Hello, <xliff:g id="name" example="Aarav">%1$s</xliff:g>!</string>

Translators see the placeholder with example context — don't accidentally translate the %1$s itself.

---

Config-qualified resources beyond strings

Layouts per orientation / size

res/layout/fragment_detail.xml           phones, portrait
res/layout-land/fragment_detail.xml      phones, landscape
res/layout-sw600dp/fragment_detail.xml   tablets

In Compose, WindowSizeClass replaces layout qualifiers for most cases — see Compose: Enterprise UX.

Colors per API level

res/values/colors.xml          pre-Android 12 fallback
res/values-v31/colors.xml       dynamic colors (Android 12+)

Animations per reduced-motion preference

No direct qualifier — query at runtime:

val reduceMotion = Settings.Global.getFloat(
    context.contentResolver, Settings.Global.ANIMATOR_DURATION_SCALE, 1f
) == 0f

Then adjust animation durations in Compose / XML.

---

Raw resources and assets

res/raw/         accessed via R.raw.*; compiled
assets/          accessed via AssetManager; loose files, any nesting

// Raw
context.resources.openRawResource(R.raw.sample_video).use { /* ... */ }

// Assets
context.assets.open("models/classifier.tflite").use { /* ... */ }

Assets are typically for large files (ML models, video), fonts, HTML pages.

---

Fonts

Resource fonts

<!-- res/font/inter.xml -->
<font-family xmlns:android="http://schemas.android.com/apk/res/android">
    <font android:fontStyle="normal" android:fontWeight="400" android:font="@font/inter_regular"/>
    <font android:fontStyle="normal" android:fontWeight="500" android:font="@font/inter_medium"/>
    <font android:fontStyle="normal" android:fontWeight="700" android:font="@font/inter_bold"/>
</font-family>

Downloadable fonts (recommended)

Fonts fetched once per device via Play Services Fonts, shared across apps:

val provider = GoogleFont.Provider(
    providerAuthority = "com.google.android.gms.fonts",
    providerPackage = "com.google.android.gms",
    certificates = R.array.com_google_android_gms_fonts_certs
)
val Inter = FontFamily(
    Font(GoogleFont("Inter"), provider, weight = FontWeight.Normal),
    Font(GoogleFont("Inter"), provider, weight = FontWeight.Medium),
    Font(GoogleFont("Inter"), provider, weight = FontWeight.Bold)
)

Saves APK size and benefits from shared caching.

---

Locale selection (in-app language switch)

Android 13+ supports per-app language:

<!-- res/xml/locales_config.xml -->
<locale-config xmlns:android="http://schemas.android.com/apk/res/android">
    <locale android:name="en"/>
    <locale android:name="es"/>
    <locale android:name="hi"/>
    <locale android:name="ar"/>
</locale-config>

<!-- AndroidManifest.xml -->
<application android:localeConfig="@xml/locales_config">

// Change at runtime
AppCompatDelegate.setApplicationLocales(LocaleListCompat.forLanguageTags("es"))

Android handles recreation, persistence, and system Settings exposure.

---

Common anti-patterns

Anti-patterns

i18n mistakes

• Hardcoded strings in Kotlin / Compose
• String concatenation for plurals
• Unnumbered %s placeholders
• left/right instead of start/end
• "$%.2f".format(price) — breaks for EUR
• No android:supportsRtl="true" in manifest

Best practices

Production i18n

• Every string in strings.xml
• Plurals via <plurals> or ICU
• Numbered %1$s, %2$d placeholders
• start/end padding, Icons.AutoMirrored
• NumberFormat.getCurrencyInstance(locale)
• supportsRtl + test in en-XA / ar-XB

---

Key takeaways

✓Resources & i18n rules

• Every user-visible string lives in strings.xml — never hardcode.
• Plurals via <plurals> — counts are locale-dependent.
• Numbered placeholders (%1$s) so translators can reorder.
• RTL-safe: start/end, autoMirrored icons, supportsRtl=true.
• Pseudo-localization (en-XA, ar-XB) catches bugs before translation.
• NumberFormat / DateTimeFormatter with device locale for numbers and dates.
• Downloadable fonts save APK size; declare per-weight in FontFamily.
• Per-app locale (Android 13+) with locales_config.xml for in-app language switching.

Practice exercises

1. 01

   Audit for hardcoded strings

   Run ./gradlew lintDebug. Fix every HardcodedText warning by moving strings to strings.xml.

2. 02

   Add plurals

   Replace a "1 item / 2 items" conditional with a <plurals> entry and getQuantityString.

3. 03

   Test pseudo-localization

   Switch device locale to en-XA. Walk through 5 screens and fix every clipped layout.

4. 04

   RTL audit

   Switch to ar-XB. Fix every left/right in padding, every non-AutoMirrored directional icon.

5. 05

   Per-app language

   Add locales_config.xml + AppCompatDelegate.setApplicationLocales. Add an in-app language picker.

Next

Return to Module 02 Overview or continue to Module 03 — Jetpack Compose.