# Text and language (/docs/reader-support/text)



Every meaningful element in an ADT page has a `data-id`. That id is the join key between the content HTML and the feature data.

<PackageSnippet title="Text-map reference" path="content/i18n/en-US/texts.json" />

## Select the display text [#select-the-display-text]

Load `content/i18n/<lang>/texts.json` for the active language. For each element in the page, replace its text with the matching value. Easy Read values use the same id with an `_easy_read` suffix.

```ts
const easyReadValue = texts[`${id}_easy_read`];
const value = easyRead && typeof easyReadValue === "string"
  ? easyReadValue
  : texts[id];
```

For images, set `alt` instead of text content. Re-apply the map after every navigation: a newly loaded document contains the original shipped text.

## Keep ids package-local [#keep-ids-package-local]

`data-id` values are ordinal and can change when the book is re-exported. Use them to join data within the package currently open, never as permanent keys for bookmarks, notes, highlights, or reader state.

<Callout type="warn" title="Respect EPUB Media Overlay targets">
  EPUB content can contain word spans targeted by SMIL. Replacing a node’s whole HTML removes those targets and breaks synchronisation. Preserve them when using Media Overlays, or use the book’s export-language text without replacing it.
</Callout>

## Discover the available languages [#discover-the-available-languages]

Read `languages.available` and `languages.default` from `assets/config.json`. The same file carries every feature flag; a `false` value means that no data was generated for that capability.

<PackageSnippet title="Feature and language configuration" path="assets/config.json" />