Albi it's little annoying when after using !sum bang you have to wait for processing of English and then click and set your language. I suggest you add bang !sum-languagecode or defaulting the language from settings in Kagi Search.
Luis You should be able to set that up with a custom bang. The query parameter used is target_language and make sure to capitalise the language code, e.g.: DE or ZH. Working example: https://kagi.com/summarizer/index.html?target_language=ZH&url=%s
