App Inventor's Yandex component does not use personal API keys. This is a special arrangement between App Inventor and Yandex.
Give that, I don't know why you'd want to use a personal key, but in any case, the translate component is not set up to do.
If for some reason, you really really want to use Yandex with a personal key, you'll have to do it by sending commands using the Web component, after registering with Yandex for a personal key.