For developers

Not a programmer? Feel free to skip this document. You don’t need to touch any code to use LingoPress: everything is done from the WordPress dashboard and is explained in the other guides (start with Getting started). This page is a technical reference, meant for anyone who wants to connect LingoPress with their own code: its functions, its “hooks” (points where you can plug in your own code) and its API.

Conventions: public functions with the lgp_ prefix, hooks with the lingopress_ prefix, namespace BallesDev\LingoPress, text domain lingopress. No Composer or external dependencies.

Public API (PHP)

Languages

Function	What it does
`lgp_languages_list( $args )`	List of the site’s languages.
`lgp_default_language( $field )`	Default language (`slug` or another field).
`lgp_current_language( $field )`	Language of the current request (frontend).
`lgp_add_language( $args )`	Creates a language (regenerates rewrite rules automatically).

Content

Function	What it does
`lgp_set_post_language( $post_id, $lang )`	Assigns a language to a post.
`lgp_get_post_language( $post_id, $field )`	Language of a post.
`lgp_save_post_translations( $translations )`	Links posts as translations (`[ 'es' => 12, 'en' => 34 ]`).
`lgp_get_post_translations( $post_id )`	Translation group of a post.
`lgp_get_post( $post_id, $lang )`	ID of a post’s translation in a given language.
`lgp_set_term_language` / `lgp_get_term_language`	Same for terms.
`lgp_save_term_translations` / `lgp_get_term_translations` / `lgp_get_term`	Same for terms.

Presentation and strings

Function	What it does
`lgp_the_languages( $args )`	Renders the language switcher (see navigation).
`lgp_register_string( $name, $text )`	Registers a translatable string in String translations.
`lgp__( $text )` / `lgp_e( $text )`	Returns / prints the translation of a registered string in the current language.
`lgp_translate_string( $text, $lang )`	Translation of a string into a specific language.

Hooks

Hook	Type	When
`lingopress_language_defined`	action	The request’s language has been resolved (frontend, on `setup_theme`).
`lingopress_ai_system_prompt`	filter	Lets you modify the system prompt sent to the AI.
`lingopress_ai_provider`	filter	Lets you replace the AI provider (inject your own).
`lingopress_switcher_items`	filter	Modifies the items of the language switcher.
`lingopress_sync_post_meta`	filter	Adds your own metadata to the sync between translations.

REST API

lang (read/write, with a capability check) and translations fields in the wp/v2/* collections of the translatable post types and taxonomies.
Filtering collections by language with ?lang=: GET /wp-json/wp/v2/posts?lang=en. lang=all disables the filter.
Custom endpoints: GET /wp-json/lingopress/v1/languages (public); POST and DELETE require manage_options.
The block editor preloads its collections already filtered by the language of the post being edited.

API keys via constants

In production, define the keys in wp-config.php — they take priority over the value stored in settings:

define( 'LINGOPRESS_ANTHROPIC_API_KEY', '...' );
define( 'LINGOPRESS_GEMINI_API_KEY', '...' );
define( 'LINGOPRESS_OPENAI_API_KEY', '...' );
define( 'LINGOPRESS_GROQ_API_KEY', '...' );

Data model

Four custom taxonomies, no custom tables: lgp_language and lgp_term_language (language of posts and terms), lgp_post_translations and lgp_term_translations (translation groups). The same model proven by Polylang, with its own prefix — it survives WXR exports/imports and can coexist with Polylang during a migration.