Localization is handled by the browser's [`Intl.RelativeTimeFormat` API](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat). No language packs are required.
The `date` attribute determines when the date/time is calculated from. It must be a string that [`Date.parse()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/parse) can interpret or a [`Date`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date) object set via JavaScript.
?> When using strings, avoid ambiguous dates such as `03/04/2020` which can be interpreted as March 4 or April 3 depending on the user's browser and locale. Instead, always use a valid [ISO 8601 date time string](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/parse#Date_Time_String_Format) to ensure the date will be parsed properly by all clients.
!> The `Intl.RelativeTimeFormat` API is available [in all major browsers](https://caniuse.com/mdn-javascript_builtins_intl_relativetimeformat), but it only became available to Safari in version 14. If you need to support Safari 13, you'll need to [use a polyfill](https://github.com/catamphetamine/relative-time-format).
You can change how the time is displayed using the `format` attribute. Note that some locales may display the same values for `narrow` and `short` formats.