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+# MSC3554: Extensible Events - Translatable Messages
+
+[MSC1767](https://github.com/matrix-org/matrix-doc/pull/1767) describes Extensible Events in detail,
+though deliberately does not include schemas for some messaging types. This MSC covers translations
+on `m.text` content blocks specifically.
+
+*Rationale*: Splitting the MSCs down into individual parts makes it easier to implement and review in
+stages without blocking other pieces of the overall idea. For example, an issue with the way images
+are represented should not block the overall schema from going through.
+
+**Note**: As a second priority MSC in the Extensible Events series, this MSC is not proposed to be a
+blocker on extensible events entering the specification - this can mean that when extensible events
+are available, translations might not be (in stable form). Readers should consider the unstable prefix
+section for early support of this MSC.
+
+## Proposal
+
+As defined by MSC1767, `m.text` currently specifies an array with "representations" for the text
+on the event. Clients are expected to find the first representation they can render based on mimetype,
+which can be implicit.
+
+Sender-provided translations can be useful in contexts where the sender knows multiple languages are
+used in a room, such as announcements or other prepared communications. Less common in instant messaging
+(at least without a translation service on the sender's side), the receiving client can use the message
+which matches the user's preferred language.
+
+This MSC adds an additional key, `lang`, to the `m.text` representation schema and adjusts how a
+client decides upon a representation to include the language in that consideration. The array overall
+is still ordered, which means the sender should also supply the language which fits the scenario best
+as the first item.
+
+An example:
+
+```json5
+{
+    "type": "m.message",
+    "content": {
+        "m.text": [
+            {
+                "body": "Je suis un poisson",
+                "lang": "fr"
+            },
+            {
+                "body": "I am a fish",
+                "lang": "en"
+            }
+        ]
+    }
+}
+```
+
+*Note*: `m.text`'s support for `mimetype` has been excluded from the example for brevity. It is still
+supported in events.
+
+By default, messages are assumed to be sent in English (`en`).
+
+`lang` must be a valid language code under [BCP-47](https://www.rfc-editor.org/rfc/bcp/bcp47.txt). This is
+in line with the HTML specification which uses a similar attribute on the `<html>` node.
+
+There is no specific guidance for when to use translation support, though cases can include automatic machine
+translation, bots with internationalization support, and possibly some bridges.
+
+## Potential issues
+
+The language code spec might not encompass all of the possible language code combinations, but should cover
+plenty given its popularity in HTML.
+
+If a sending client supports several languages, receiving clients could spend extra time attempting to find
+a suitable representation to render. This is considered a non-issue, though clients should consider how to
+efficiently search an array.
+
+## Alternatives
+
+No significant alternatives known.
+
+## Security considerations
+
+No specific considerations are required for this proposal.
+
+## Unstable prefix
+
+While this MSC is not considered stable, implementations should use `org.matrix.msc3554.lang` instead of `lang`
+when sending events.
+
+Note that extensible events should only be used in an appropriate room version as well.