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Localization, formatting, plurals, and RTL

Translate messages, not fragments​

❌ Concatenation assumes English order:

Text("Hello " + userName + ", you have " + count + " messages")

✅ Give translators one complete resource with placeholders:

<string name="inbox_greeting">Hello %1$s, you have %2$d messages</string>

For quantities, use plurals because grammatical rules differ by locale:

<plurals name="message_count">
    <item quantity="one">%d message</item>
    <item quantity="other">%d messages</item>
</plurals>
val label = pluralStringResource(R.plurals.message_count, count, count)

Zero is not universally a special plural category; use Android/CLDR rules rather than if (count == 1) scattered through code.

Formatting belongs to locale-aware APIs​

Do not hardcode "$1,234.50", dd/MM/yyyy, commas, or string capitalization. Use currency/number/date formatting with the intended locale and time zone. Store instants and numeric values structurally; format at the presentation edge.

val priceLabel = NumberFormat.getCurrencyInstance(locale).apply {
    currency = Currency.getInstance(currencyCode)
}.format(amount)

The currency code must come from business data; device locale alone cannot tell whether a transaction is USD or INR.

RTL is more than mirrored text​

  • Use start/end, not left/right, for layout intent.
  • Directional icons such as back/forward often mirror; clocks, media play, and brand marks often do not.
  • Test mixed-direction content such as Arabic text containing an email or phone number.
  • Avoid baking text into images.

Pseudolocales expose bugs early​

en-XA expands/accentuates text and exposes hardcoding. ar-XB simulates RTL. Enable them in debug builds and include screenshots/UI checks in CI for important screens.

android {
    buildTypes.debug { isPseudoLocalesEnabled = true }
}
Resource completeness

Every referenced resource needs a default value. A translated directory may be partial; the unqualified default set must remain complete or some configurations can crash.

Sources​

Interview exercises​

  1. Localize “1 file deleted” and “5 files deleted.”
  2. Explain why device locale cannot choose a transaction currency.
  3. Review a checkout UI for RTL and text-expansion failures.