How to Translate Messages using the ICU MessageFormat
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How to Translate Messages using the ICU MessageFormat
4.2
Support for ICU MessageFormat was introduced in Symfony 4.2.
Messages (i.e. strings) in applications are almost never completely static. They contain variables or other complex logic like pluralization. In order to handle this, the Translator component supports the ICU MessageFormat syntax.
Tip
You can test out examples of the ICU MessageFormatter in this online editor.
Using the ICU Message Format
In order to use the ICU Message Format, the message domain has to be suffixed with +intl-icu:
| Normal file name | ICU Message Format filename |
|---|---|
messages.en.yaml |
messages+intl-icu.en.yaml |
messages.fr_FR.xlf |
messages+intl-icu.fr_FR.xlf |
admin.en.yaml |
admin+intl-icu.en.yaml |
All messages in this file will now be processed by the MessageFormatter during translation.
Message Placeholders
The basic usage of the MessageFormat allows you to use placeholders (called arguments in ICU MessageFormat) in your messages:
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# translations/messages+intl-icu.en.yaml
say_hello: 'Hello {name}!'Everything within the curly braces ({...}) is processed by the formatter
and replaced by its placeholder:
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// prints "Hello Fabien!"
echo $translator->trans('say_hello', ['name' => 'Fabien']);
// prints "Hello Symfony!"
echo $translator->trans('say_hello', ['name' => 'Symfony']);Selecting Different Messages Based on a Condition
The curly brace syntax allows to "modify" the output of the variable. One of
these functions is the select function. It acts like PHP's switch statement
and allows to use different strings based on the value of the variable. A
typical usage of this is gender:
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# translations/messages+intl-icu.en.yaml
invitation_title: >
{organizer_gender, select,
female {{organizer_name} has invited you for her party!}
male {{organizer_name} has invited you for his party!}
other {{organizer_name} have invited you for their party!}
}This might look very complex. The basic syntax for all functions is
{variable_name, function_name, function_statement} (where, as you see
later, function_statement is optional for some functions). In this case,
the function name is select and its statement contains the "cases" of this
select. This function is applied over the organizer_gender variable:
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// prints "Ryan has invited you for his party!"
echo $translator->trans('invitation_title', [
'organizer_name' => 'Ryan',
'organizer_gender' => 'male',
]);
// prints "John & Jane have invited you for their party!"
echo $translator->trans('invitation_title', [
'organizer_name' => 'John & Jane',
'organizer_gender' => 'not_applicable',
]);The {...} syntax alternates between "literal" and "code" mode. This allows
you to use literal text in the select statements:
- The first
{organizer_gender, select, ...}block starts the "code" mode, which meansorganizer_genderis processed as a variable. - The inner
{... has invited you for her party!}block brings you back in "literal" mode, meaning the text is not processed. - Inside this block,
{organizer_name}starts "code" mode again, allowingorganizer_nameto be processed as variable.
Tip
While it might seem more logical to only put her, his or their
in the switch statement, it is better to use "complex arguments" at the
outermost structure of the message. The strings are in this way better
readable for translators and, as you can see in the other case, other
parts of the sentence might be influenced by the variables.
Pluralization
Another interesting function is plural. It allows you to
handle pluralization in your messages (e.g. There are 3 apples vs
There is one apple). The function looks very similar to the select function:
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# translations/messages+intl-icu.en.yaml
num_of_apples: >
{apples, plural,
=0 {There are no apples}
one {There is one apple...}
other {There are # apples!}
}Pluralization rules are actually quite complex and differ for each language. For instance, Russian uses different plural forms for numbers ending with 1; numbers ending with 2, 3 or 4; numbers ending with 5, 6, 7, 8 or 9; and even some exceptions of this!
In order to properly translate this, the possible cases in the plural
function are also different for each language. For instance, Russian has
one, few, many and other, while English has only one and
other. The full list of possible cases can be found in Unicode's
Language Plural Rules document. By prefixing with =, you can match exact
values (like 0 in the above example).
Usage of this string is the same as with variables and select:
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// prints "There is one apple..."
echo $translator->trans('num_of_apples', ['apples' => 1]);
// prints "There are 23 apples!"
echo $translator->trans('num_of_apples', ['apples' => 23]);Note
You can also set an offset variable to determine whether the
pluralization should be offset (e.g. in sentences like You and # other people
/ You and # other person).
Tip
When combining the select and plural functions, try to still have
select as outermost function:
- {gender_of_host, select,
-
- female {
- {num_guests, plural, offset:1 =0 {{host} does not give a party.} =1 {{host} invites {guest} to her party.} =2 {{host} invites {guest} and one other person to her party.} other {{host} invites {guest} and # other people to her party.}}
} male { {num_guests, plural, offset:1 =0 {{host} does not give a party.} =1 {{host} invites {guest} to his party.} =2 {{host} invites {guest} and one other person to his party.} other {{host} invites {guest} and # other people to his party.}} } other { {num_guests, plural, offset:1 =0 {{host} does not give a party.} =1 {{host} invites {guest} to their party.} =2 {{host} invites {guest} and one other person to their party.} other {{host} invites {guest} and # other people to their party.}} }
Additional Placeholder Functions
Besides these, the ICU MessageFormat comes with a couple other interesting functions.
Ordinal
Similar to plural, selectordinal allows you to use numbers as ordinal scale:
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# translations/messages+intl-icu.en.yaml
finish_place: >
You finished {place, selectordinal,
one {#st}
two {#nd}
few {#rd}
other {#th}
}!
# when only formatting the number as ordinal (like above), you can also
# use the `ordinal` function:
finish_place: You finished {place, ordinal}!1 2 3 4 5 6 7 8
// prints "You finished 1st!"
echo $translator->trans('finish_place', ['place' => 1]);
// prints "You finished 9th!"
echo $translator->trans('finish_place', ['place' => 9]);
// prints "You finished 23rd!"
echo $translator->trans('finish_place', ['place' => 23]);The possible cases for this are also shown in Unicode's Language Plural Rules document.
Date and Time
The date and time function allows you to format dates in the target locale using the IntlDateFormatter:
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# translations/messages+intl-icu.en.yaml
published_at: 'Published at {publication_date, date} - {publication_date, time, short}'The "function statement" for the time and date functions can be one of
short, medium, long or full, which correspond to the
constants defined by the IntlDateFormatter class:
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// prints "Published at Jan 25, 2019 - 11:30 AM"
echo $translator->trans('published_at', ['publication_date' => new \DateTime('2019-01-25 11:30:00')]);Numbers
The number formatter allows you to format numbers using Intl's NumberFormatter:
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# translations/messages+intl-icu.en.yaml
progress: '{progress, number, percent} of the work is done'
value_of_object: 'This artifact is worth {value, number, currency}'1 2 3 4 5 6 7 8 9
// prints "82% of the work is done"
echo $translator->trans('progress', ['progress' => 0.82]);
// prints "100% of the work is done"
echo $translator->trans('progress', ['progress' => 1]);
// prints "This artifact is worth $9,988,776.65"
// if we would translate this to i.e. French, the value would be shown as
// "9 988 776,65 €"
echo $translator->trans('value_of_object', ['value' => 9988776.65]);
