Add device trigger translation documentation (#734)

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

docs/device_automation_trigger.md

@@ -5,13 +5,14 @@ sidebar_label: Triggers
 
 Device triggers are automation triggers that are tied to a specific device and an event or state change. Examples are "light turned on" or "water detected".
 
-Device triggers can be provided by the integration that provides the device (e.g. ZHA, deCONZ) or the entity integrations that the device has entities with (e.g. light, switch).  An example of the former is events not tied to an entity e.g. key press on a remote control or touch panel, while an example of the latter could be that a light has been turned on.
+Device triggers can be provided by the integration that provides the device (e.g. ZHA, deCONZ) or the entity integrations that the device has entities with (e.g. light, switch). An example of the former is events not tied to an entity e.g. key press on a remote control or touch panel, while an example of the latter could be that a light has been turned on.
 
 To add support for Device Triggers, an integration needs to have a `device_trigger.py` and:
 
 - *Define a `TRIGGER_SCHEMA`*: A dictionary that represents a trigger, such as a device and an event type
 - *Create triggers*: Create dictionaries containing the device or entity and supported events or state changes as defined by the schema.
 - *Attach triggers*: Associate a trigger config with an event or state change, e.g. a message fired on the event bus.
+- *Add text and translations*: Give each trigger a human readable name. 
 
 Home Assistant includes a template to get started with device triggers. To get started, run inside a development environment `python3 -m script.scaffold device_trigger`.
 
@@ -77,7 +78,7 @@ async def async_get_triggers(hass, device_id):
 
 #### Attach triggers
 
-The last step is to wire everything up: Given a `TRIGGER_SCHEMA` config, make sure the `action` is called when the trigger is triggered.
+To wire it up: Given a `TRIGGER_SCHEMA` config, make sure the `action` is called when the trigger is triggered.
 
 For example, you might attach the trigger and action to [Events fired](integration_events.md) on the event bus by your integration.
 
@@ -99,3 +100,18 @@ async def async_attach_trigger(hass, config, action, automation_info):
 ```
 
 The return value is a function that detaches the trigger.
+
+#### Add text and translations
+
+The Automation user interface will display a human-readable string in the device automation mapped to the event
+type.  Update `strings.json` and if you used `script.scaffold` then `translations/en.json` with the full set of supported event types:
+
+```json
+{
+   "device_automation": {
+    "trigger_type": {
+      "water_detected": "Water detected",
+      "noise_detected": "Noise detected"
+    }
+}
+```