Add blogpost about translation placeholders (#2046)

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

blog/2024-01-19-entity-translations-placeholders.md

@@ -0,0 +1,44 @@
+---
+author: Joost Lekkerkerker
+authorURL: https://github.com/joostlek
+authorImageURL: https://avatars.githubusercontent.com/u/7083755?v=4
+title: "Introducing entity translation placeholders"
+---
+
+It's now possible to provide static values to be used in an entity translation using placeholders.
+You can pass placeholders via the `translation_placeholders` property of an entity.
+
+An example sensor:
+```python
+class TestEntity(SensorEntity):
+    """Example entity."""
+    
+    _attr_has_entity_name = True
+    _attr_translation_key = "temperature"
+    
+    def __init__(self) -> None:
+        """Initialize example entity."""
+        self._attr_translation_placeholders = {"channel_id": "2"}
+        self._attr_device_info = DeviceInfo(
+            name="Example device"
+        )
+```
+The `strings.json` file would look like:
+```json
+{
+  "entity": {
+    "sensor": {
+      "temperature": {
+        "name": "Temperature channel {channel_id}"
+      }
+    }
+  }
+}
+```
+
+The resulting entity would be called `Example device Temperature channel 2`.
+
+A warning is logged once when a translation placeholder is expected but not provided by the entity.
+When this happens on a system that is not on a stable version (dev, nightly, or beta), an error will be raised to be able to catch the mistakes quickly.
+
+Please don't forget to be kind towards your translators, as they need to understand what kind of name or value will be passed in from the placeholder name ❤️.