add documentation

website/docs/ref/core.md

@@ -115,16 +115,32 @@ Formatting of messages as strings (e.g: `"My name is {name}"`) works in developm
 The same example would in real application look like this:
 
 ```ts
-import { i18n } from "@lingui/core"
+import { i18n } from "@lingui/core";
 
 // File generated by `lingui compile`
-import { messages: messagesEn } from "./locale/en/messages.js"
+import { messages as messagesEn } from "./locale/en/messages.js";
 
-i18n.load('en', messagesEn)
+i18n.load("en", messagesEn);
 ```
 
 :::
 
+### `i18n.setMessagesCompiler(compiler)` {#i18n.setMessagesCompiler}
+
+Registers a `MessageCompiler` to enable the use of uncompiled catalogs at runtime.
+
+In production builds, the `MessageCompiler` is typically excluded to reduce bundle size.
+
+By default, message catalogs should be precompiled during the build process. However, if you need to compile catalogs at runtime, you can use this method to set a message compiler.
+
+Example usage:
+
+```ts
+import { compileMessage } from "@lingui/message-utils/compileMessage";
+
+i18n.setMessagesCompiler(compileMessage);
+```
+
 ### `i18n.activate(locale[, locales])` {#i18n.activate}
 
 Activate a locale and locales. From now on, calling `i18n._` will return messages in given locale.