Localization

By the end of this lesson you'll build multilingual PHP apps: a translation system with placeholders, correct plurals for every language, locale-aware money and dates with the intl extension, and automatic language detection — without hardcoding a single string.

Part of the free Php course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

What You'll Learn in This Lesson

1️⃣ Translation Systems: Never Hardcode Text

The single most important habit in i18n is to separate text from code . Instead of writing echo "Welcome!" , you store every user-facing string in a message file under a key like welcome , then look it up: t('welcome') . A placeholder such as :name is a slot you fill at runtime, so "Hello, :name!" becomes "¡Hola, Alice!" in Spanish. The ?? operator below is the null-coalescing operator — "use the left value, or the right one if it's missing" — which gives you a clean fallback chain.

Notice that the code never changed between locales — only the data did. That is i18n (the structure) and l10n (the Spanish array) working together. Real apps load these arrays from per-language files ( en.php , es.php , or JSON), which is exactly how Laravel and Symfony work under the hood.

2️⃣ setlocale, gettext & the UTF-8 Rule

PHP's classic localization tools are setlocale() and gettext . setlocale(LC_MONETARY, 'de_DE.UTF-8') changes how some built-in functions behave, but it depends on locales being installed on the server , so it's fragile — prefer the intl extension in the next section. gettext is the GNU translation standard: you wrap text in _('Welcome') and ship compiled .mo files per language. Whichever you choose, the non-negotiable rule is UTF-8 everywhere — and to count or cut non-ASCII text you must use the multibyte mb_ functions, because the plain ones work in bytes , not characters.

See the difference? strlen reports 13 because the accented letters take two bytes each in UTF-8, while mb_strlen correctly reports 12 characters. Get this wrong and you'll slice a character in half and produce mojibake — those garbled é symbols.

3️⃣ The intl Extension: Currency, Dates & Locale Detection

The same number is written completely differently around the world: 1,234,567.89 in the US is 1.234.567,89 in Germany, and Japanese yen has no decimal places at all. PHP's intl extension wraps ICU — the industry-standard Unicode library — so NumberFormatter and IntlDateFormatter apply each locale's real rules for you, including the correct currency symbol and its position. Dates also need a time zone : always store times in UTC, then convert to the visitor's zone when you display them.

The detectLocale() function shows the priority order professionals use: an explicit choice ( ?lang=fr or a /fr/ URL prefix) beats a saved cookie, which beats the browser's Accept-Language header, which beats a default. Locale::acceptFromHttp() parses that messy header ( fr-CH,fr;q=0.9,en;q=0.8 ) and returns the best match.

4️⃣ Plurals Done Right with MessageFormatter

"5 items" feels trivial in English, but plural rules vary enormously: English has 2 forms, Polish has 3 (for 1, for 2–4, and for 5+), and Arabic has 6 . If you write $n === 1 ? 'item' : 'items' you've baked English grammar into your code and it will be wrong everywhere else. MessageFormatter uses ICU's {count, plural, ...} syntax, reads the locale's plural rules, and picks the right form — the # is replaced by the number, formatted for that locale.

5️⃣ Your Turn: Translate & Format

Now you drive. The first script is almost complete — fill in each ___ using the 👉 hint, then run it and check it against the Output panel.

One more. This time you'll format the same price as two currencies with NumberFormatter . Fill in the locale and the formatter type.

Common Errors (and the fix)

• Hardcoded or concatenated strings — echo "You have " . $count . " items" can't be translated and breaks where word order differs. Move the whole sentence into a message file with a placeholder: t('cart.items', ['count' => $count]) .
• Wrong plural rules — $n === 1 ? 'item' : 'items' bakes in English grammar and fails in Polish, Arabic, Russian, etc. Use MessageFormatter with a {count, plural, ...} pattern so ICU picks the right form.
• Accents become é or ? (mojibake) — an encoding mismatch. Save files as UTF-8, send charset=UTF-8 , call mb_internal_encoding('UTF-8') , and use utf8mb4 in MySQL. Count/cut text with mb_strlen / mb_substr , never strlen / substr .
• "Class 'NumberFormatter' not found" — the intl extension isn't enabled. Enable extension=intl in php.ini (or apt install php-intl ); check with php -m | grep intl .
• Currency formatting with number_format() — it forces you to hardcode the symbol, separators, and decimal count, which you'll get wrong for locales you don't speak (and yen has no decimals). Use $fmt->formatCurrency($amount, 'EUR') instead.

Pro Tips

• 💡 Use URL prefixes ( /fr/products ) over ?lang=fr — search engines index each language as its own page, and you can add hreflang tags so Google serves the right one.
• 💡 Store all times in UTC and convert to the visitor's zone only when displaying. Mixing zones in storage is a classic source of "off by a day" bugs.
• 💡 Plan for RTL. Arabic, Hebrew, Persian, and Urdu read right-to-left. Set dir="rtl" and lang="ar" on <html> , use CSS logical properties ( margin-inline-start , not margin-left ), and let the browser mirror the layout.
• 💡 Always give translators context. A key like button.save beats save — the same English word can need different translations as a noun vs a verb.

📋 Quick Reference — Localization

Tool

Example

What It Does

NumberFormatter

$f->formatCurrency($n,'EUR')

Locale-aware money / numbers / percent

IntlDateFormatter

$d->format($date)

Locale & timezone-aware dates

MessageFormatter

::formatMessage($loc,$p,$args)

Correct plurals per language

Locale::acceptFromHttp

(...$_SERVER['HTTP_ACCEPT_LANGUAGE'])

Best locale from the browser header

setlocale / gettext

_('Welcome')

Classic GNU translation system

mb_strlen / mb_substr

mb_strlen($s)

Count / cut by character, not byte (UTF-8)

Frequently Asked Questions

Mini-Challenge: Order Summary

No code is filled in this time — just a brief and an outline. Write it yourself, run it on onecompiler.com/php or your own machine, then check your result against the expected output in the comments. This combines a plural phrase and a currency format — exactly the write-run-check loop you'll use on real localized features.

🎉 Lesson Complete!

• ✅ i18n makes code language-capable; l10n supplies each language's translations and formats
• ✅ Never hardcode text — look it up by key with :placeholder slots and a fallback locale
• ✅ Use the intl extension: NumberFormatter for money, IntlDateFormatter for dates (always store UTC)
• ✅ MessageFormatter picks the correct plural form for any language
• ✅ Detect locale in priority order (URL → cookie → Accept-Language → default), and plan for RTL
• ✅ Keep everything UTF-8 and reach for the mb_ string functions
• ✅ Next lesson: Search Features — add full-text search and Elasticsearch to your app

Practice quiz

Continue this course

• Previous: PDF Generation
• Next: Search Features

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