Make unknown media source exception translatable

homeassistant/components/media_source/__init__.py

@@ -33,7 +33,7 @@ from .const import (
     URI_SCHEME,
     URI_SCHEME_REGEX,
 )
-from .error import MediaSourceError, Unresolvable
+from .error import MediaSourceError, UnknownMediaSource, Unresolvable
 from .models import BrowseMediaSource, MediaSource, MediaSourceItem, PlayMedia
 
 __all__ = [
@@ -113,7 +113,11 @@ def _get_media_item(
         return MediaSourceItem(hass, domain, "", target_media_player)
 
     if item.domain is not None and item.domain not in hass.data[DOMAIN]:
-        raise ValueError("Unknown media source")
+        raise UnknownMediaSource(
+            translation_domain=DOMAIN,
+            translation_key="unknown_media_source",
+            translation_placeholders={"domain": item.domain},
+        )
 
     return item
 

homeassistant/components/media_source/error.py

@@ -9,3 +9,7 @@ class MediaSourceError(HomeAssistantError):
 
 class Unresolvable(MediaSourceError):
     """When media ID is not resolvable."""
+
+
+class UnknownMediaSource(MediaSourceError, ValueError):
+    """When media source is unknown."""

homeassistant/components/media_source/strings.json

@@ -0,0 +1,7 @@
+{
+  "exceptions": {
+    "unknown_media_source": {
+      "message": "Unknown media source: {domain}"
+    }
+  }
+}