Hello,
Can you please tell me which one of the following sentences would you choose as the more used one or the correct one ?
You've never mentioned having lived in Japan before.
You've never mentioned living in Japan before
Thank you for your help
Both are acceptable, in my opinion. I think that most native speakers today would use the second, although it is possible to take it to mean that you do live in Japan now.
If you want to make your meaning absolutely clear, then use the appropriate one of these:
You've never mentioned that you live in Japan.
You've never mentioned that you used to live in Japan.