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Internationalization and localization adapt the applications and their contents to the specific region or language of the users. In Symfony this is an opt-in feature that needs to be installed before using it (composer require symfony/translation).

Translation Source File Location

Best Practice

Store the translation files in the translations/ directory at the root of your project.

Your translators' lives will be much easier if all the application translations are in one central location.

Translation Source File Format

The Symfony Translation component supports lots of different translation formats: PHP, Qt, .po, .mo, JSON, CSV, INI, etc.

Best Practice

Use the XLIFF format for your translation files.

Of all the available translation formats, only XLIFF and gettext have broad support in the tools used by professional translators. And since it's based on XML, you can validate XLIFF file contents as you write them.

Symfony supports notes in XLIFF files, making them more user-friendly for translators. At the end, good translations are all about context, and these XLIFF notes allow you to define that context.


The PHP Translation Bundle includes advanced extractors that can read your project and automatically update the XLIFF files.

Translation Keys

Best Practice

Always use keys for translations instead of content strings.

Using keys simplifies the management of the translation files because you can change the original contents without having to update all of the translation files.

Keys should always describe their purpose and not their location. For example, if a form has a field with the label "Username", then a nice key would be label.username, not edit_form.label.username.

Example Translation File

Applying all the previous best practices, the sample translation file for English in the application would be:

<!-- translations/messages.en.xlf -->
<?xml version="1.0"?>
<xliff version="1.2" xmlns="urn:oasis:names:tc:xliff:document:1.2">
    <file source-language="en" target-language="en" datatype="plaintext" original="file.ext">
            <trans-unit id="title_post_list">
                <target>Post List</target>

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