IceCreamKid hits it on the head - was this actually Chinese/Japanese, that is to say, was the relative able to communicate with Chinese/Japanese speakers in their own language? Linguistic research has shown that young children who watch TV in a foreign language don't acquire the language, as opposed to, for instance, children who have a babysitter or au pair who interact with them in a foreign language. Interaction and/or conscious volition are key: you don't learn a language well enough to communicate unless you either interact in it or else are consciously trying to acquire it (when you watch a film with subtitles, for instance.)

Magic or spiritual influences are a different matter, which (unlike the linguistics issue) I'm not competent to comment on.