Localization means that an application (or homepage) can be used from different users which speak different languages. But as you already have expected Localization means more than only translating strings. It includes

Each computer user makes use of Locales, even when they don't know it. Applications lacking localization support, normally have implicit support for one particular locale (the locale of the author). When a class or function makes use of localization, we say it is locale-aware. How does the code know which localization the user is expecting?

A locale string or object identifying a supported locale gives Zend_Locale and it's subclasses access to information about the language and region expected by the user. Correct formatting, normalization, and conversions are made based on this information.

Locale identifiers consist of information about the user's language and preferred/primary geographic region (e.g. state or province of home or workplace). The locale identifier strings used in the Zend Framework are internationally defined standard abbreviations of language and region, written as language_REGION. Both the language and region parts are abbreviated to 2 alphabetic, ASCII characters.

A user from USA would expect the language English and the region USA, yielding the locale identifier "en_US". A user in Germany would expect the language German and the region Germany, yielding the locale identifier "de_DE". See the list of pre-defined locale and region combinations , if you need to select a specific locale within the Zend Framework.

<?php
require_once 'Zend_Locale');
$locale = new Zend_Locale('de_DE'); // German language _ Germany
?>

A German user in America might expect the language German and the region USA, but these non-standard mixes are not supported directly as recognized "locales". Instead, if an invalid combination is used, then it will automatically be truncated by dropping the region code. For example, "de_IS" would be truncated to "de", and "xh_RU" would be truncated to "xh", because neither of these combinations are valid. Additionally, if the base language code is not supported (e.g. "zz_US") or does not exist, then a default "root" locale will be used. The "root" locale has default definitions for internationally recognized representations of dates, times, numbers, currencies, etc. The truncation process depends on the requested information, since some combinations of language and region might be valid for one type of data (e.g. dates), but not for another (e.g. currency format).

Beware of historical changes, as ZF components do not know about or attempt to track the numerous timezone changes made over many years by many regions. For example, we can see a historical list showing dozens of changes made by governments to when and if a particular region observes Daylight Savings Time, and even which timezone a particular geographic area belongs. Thus, when performing date math, the math performed by ZF components will not adjust for these changes, but instead will give the correct time for the timezone using current, modern rules for DST and timezone assignment for geographic regions.

For most situations, new Zend_Locale() will automatically select the correct locale, with preference given to information provided by the user's web browser. However, if new Zend_Locale(Zend_Locale::ENVIRONMENT) is used, then preference will be given to using the host server's environment configuration, as described below.

<?php
require_once 'Zend/Locale.php';
$locale  = new Zend_Locale();
$locale1 = new Zend_Locale(Zend_Locale::BROWSER);     // default behavior, same as above
$locale2 = new Zend_Locale(Zend_Locale::ENVIRONMENT); // prefer settings on host server
$locale3 = new Zend_Locale(Zend_Locale::FRAMEWORK);   // perfer framework app default settings
?>

The seach algorithm used by Zend_Locale for automatic selection of a locale uses three sources of information:

In the ZF, locale-aware classes rely on Zend_Locale to automatically select a locale, as explained above. For example, in a ZF web application, constructing a date using Zend_Date without specifying a locale results in an object with a locale based on information provided by the current user's web browser.

<?php
require_once 'Zend/Date.php';
$date = new Zend_Date('2006',Zend_Date::YEAR);
?>

To override this default behavior, and force locale-aware ZF components to use specific locales, regardless of the origin of your website visitors, explicitly specify a locale as the third argument to the constructor.

<?php
require_once 'Zend/Date.php';
require_once 'Zend/Measure/Temperature.php';

$usLocale = new Zend_Locale('en_US');
$date = new Zend_Date('2006',Zend_Date::YEAR, $usLocale);
$temp = new Zend_Measure_Temperature('100,10',Zend_Measure::TEMPERATURE, $usLocale);
?>

If you know many objects should all use the same default locale, explicitly specify the default locale to avoid the overhead of each object determining the default locale.

<?php
require_once 'Zend/Date.php';
require_once 'Zend/Measure/Temperature.php';

$locale = new Zend_Locale();
$date = new Zend_Date('2006',Zend_Date::YEAR, $locale);
$temp = new Zend_Measure_Temperature('100,10',Zend_Measure::TEMPERATURE, $locale);
?>

The 'precision' option of a value is used to truncate or stretch extra digits. A value of '-1' disables modification of the number of digits in the fractional part of the value. The 'locale' option helps when parsing numbers and dates using separators and month names. The date format 'type' option selects between CLDR/ISO date format specifier tokens and PHP's date() tokens. The 'fix_date' option enables or disables heuristics that attempt to correct invalid dates. The 'number_format' option specifies a default number format for use with toNumber() (see Seção 18.3.2, “Number localization” ).

The 'date_format' option can be used to specify a default date format string, but beware of using getDate(), isDate(), getTime(), and isTime() after using setOptions() with a 'date_format'. To use these four methods with the default date format for a locale, use array('date_format' => null, 'locale' => $locale) for their options.

<?php
require_once 'Zend/Locale.php';
Zend_Locale_Format::setOptions('locale' => 'en_US', 'fixdate' => true, 'type' => 'php');
?>