feat(translator): add source language detected automatically if no la…

…ng provided

lib/translator.ai.yaml

@@ -3,7 +3,15 @@ type: lib
 version: 0.1.0
 name: "Translator"
 description: |-
-  translate the content to the target language.
+  Translate the content or a file to the target language.
+  It can be used in prompt. eg, `Translate: @translator(file='document.md', target='English')`
+
+  Or, run it directly:
+
+  ```bash
+  # `no-chats` means do not save this into chat history
+  $ai run --no-chats -f translator "{content:'我爱我的祖国和故乡.', target: 'English'}"
+  ````
 tag:
   - translate
   - translator
@@ -52,6 +60,10 @@ parameters:
 - $if: "this.content"
   then:
     # For API mode.
+    - $if: "!this.lang || this.lang === 'auto'"
+      then:
+        $set:
+          lang: "?=this.$detectLang(content.slice(0, 120))"
     - user: |-
         Output high-quality translation result before the completion delimiter "{{completion_delimiter}}".
         {%- if content.length > 50 -%}