[mod] settings.yml: enable language detection by default_lang (auto)

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/settings.yml

@@ -31,7 +31,7 @@ search:
   autocomplete_min: 4
   # Default search language - leave blank to detect from browser information or
   # use codes from 'languages.py'
-  default_lang: ""
+  default_lang: "auto"
   # Available languages
   # languages:
   #   - all