"Ken" derives from Middle English but, as far as I know, is chiefly a word used colloquially by the Scottish, which is probably why Google translate doesn't handle it correctly. As a (more or less) regional colloquialism you probably shouldn't use it unless you're deliberately trying to imitate people from that region, otherwise it'll feel forced and unnatural.
Also, not everyone will understand "ken" or "beyond my ken", unless they've heard it before and recognize the idiom.
I most commonly see "ken" in writing from authors who are trying to imitate a Scottish accent, "I dinna (don't) ken what yer (you're) sayin', lassie (young female), because I'm a wee (little) bit deaf in my right ear" and so on.
Note this isn't necessarily an accurate representation of how the Scottish accent sounds. It's just the way it's often popularized. If you're unfamiliar with the Scottish accent I recommend you look up videos on YouTube. There are actually many different accents from around the Northern part of the U.K., some of which are difficult to understand for anyone who isn't a local.