There’s nothing like a limited release Japanese promo. I try to stick with the English versions for set cards.
Englsih sets and Japanese specific promos, boxes and releases.
Those are what I personally focus on, however it is up to you depending on your collecting goals.
Another way is purely, if you like it…buy it(aslong as you arent being ripped off). If the future value isn’t important and you just want artwork…you can buy some really nice unique cards pretty cheap. Especially Japanese set cards as the Japanese card art can be truly amazing.