Champion: Unknown

Revision: latest

RFC created: 1970/01/01

Last updated: unknown

This RFC has been merged


Provide best-in-class localization infrastructure for Lightning Web Components.

Use Cases

Proposal 1: Fluent Subset

This proposal is heavily influenced by Fluent from Mozilla. And introduces a new template directive called intl that can be use to specify certain things in the template.

The most basic step is to define the id of the translation bundle by using <template intl:id="something">, which means that the template can be localized/localized by parsing the HTML, and extracting the labels from it. This signals to the compiler that extra work is required during compilation to extra all the labels and produce a localization bundle per component.

Template Grammar

The template grammar is following a simplified Fluent grammar by adding certain restrictions.


Lightning Web Components already support interpolation in the body of the tags by using {identifier}, with no spaces, and where the identifier must be a JavaScript valid identifier. Additionally, you can reference any property member, e.g.: {}.

Additionally, interpolation of text and HTML markup is supported. e.g.:

<template intl:id="bundle1">
    <p>Age: <b>{state.userAge}</b></p>

Built-in Functions

Like Fluent, we want to provide a set of standard built-in functions that can be used as part of the interpolation and value normalization.

PLURAL() built-in function

Function that receives a number, and produces "zero", "one", "two", "few", "many" or "other". Additionally, it supports an argument type, which could be ordinal or cardinal (default value).

PLURAL(value, type: "cardinal")
PLURAL(value, type: "ordinal")
NOUN() built-in function

Function that receives the name of the noun as a string, and produces the corresponding form based on a set of options.

NOUN("opportunity", plural: "y")

The first argument is the name of the noun (will be used as a fallback value). The rest of the arguments are optional key: value pairs:

Optional attributes:

Note: if no attributes specified, the default value is equivalent to:

NOUN("opportunity", case: "n", plural: "n", article: "n")


<template intl:id="bundle2">
    <p>Allows collection of {NOUN("chatter")} and {NOUN("networks")} metrics</p>
    <label>Enable announcements in {NOUN("Chatter")}</label>
    <p>You need to specify {NOUN("contact"), article: "a")} on {NOUN("case", article: "the")} first.</p>


This is the more generic form of logic in a template, equivalent to switch in JavaScript where the value state.usergender is going to be matched against the 3 provided options:

<template intl:id="bundle3">
    <p>{state.userName} liked your comment on {state.usergender ->
        [male] his
        [female] her
       *[other] their
    } post.

The option marked with * is the default. Also note that the example is using interpolation in combination with the selection mechanism, so a segment of the overall text will be driven by the value of state.usergender.


The pluralization is just a more specific selection mechanism by using the PLURAL() built-in function to transform a numeric value to match one of the following values: "zero", "one", "two", "few", "many" or "other". The rest is just the regular selection mechanism.

<template intl:id="bundle4">
    <p>{PLURAL( ->
        [zero] User hasn't added any photos yet
        [one] User added a new photo
        *[other] User added {NUMBER(} new photos


This proposal does not include any advanced option for HTML attributes. Which means that built-in functions and advanced interpolation are not possible for HTML attribute. However, it does exact certain elements and attributes that are allowed for localization. E.g.:

<template intl:id="bundle5">
    <button title="click here to show more details" class="big">

In the example above, the title of the <button> and the text, can be localized, while the class attribute should not.

For custom elements, since we do not know what is localizable or not, the developer can signal it by using the intl directive:

<template intl:id="bundle6">
    <fancy-button class="big" intl:tooltip="click here to show more details">

In the example above, even though the compiler does not know what tooltip attributes is, it will extract it for localization because it is marked with the intl: directive.

Lightning Web Components vs Fluent

As we mentioned above, Lightning Web Components template uses a more restrictive grammar, where:



just a label

  1. "Expand"
  2. "What I Follow"

label with token replacement

  1. "W-4157973 — John Smith to GUS Only"

where "W-4157973" and "John Smith" are computed values.

label with pluralization rules

  1. "240 Members"

where "members" is pluralized depending on the numeric value.

label with genre select rules

  1. "Kimberly Lee, Vinit Bhandari, and 12 others like this."

where the number of users have to be separated, counted, and the offset for the numeric value of "12" have to be formatted, and "others" must be pluralized.

label with number (ordinals)

  1. "Popular group: 3,078 members"
  2. "240 Members"

where "3,078" is a formatted number, and "members" is pluralized.

label with currency


label with date-time

  1. "Last Modified By UserAgile Health, 8/16/2017 1:00 AM"

label with relative time

  1. "Joined in the last month"

where "last month" is a relative time formatted value

  1. "50+ items • Updated a few seconds ago"

where "a few seconds ago" is a relative time formatted value, and "50+ items" is a number formatted value with pluralization.

label with dynamic entities

  1. "You need to specify a contact on the case first."

where "a contact" is an entitity (<contact article="a"/>) and "the case" is an entitye as well (<case article="the"/>).

label with embeded HTML (including attributes)

  1. "<strong>Note:</strong> See Merge Fields Below"

where "<strong>Note:</strong>" is a markup segment, and only "Note:" should be localized.

  1. "In the <a href="/item/number/123">example below</a>, "Sir or Madam" will be substituted if the lead doesn't have a first name."

where "/item/number/123" is a computed value, and all other visible text should be localized.