There has been some discussion of late regarding what is and is not a JRPG, notably over if it is a JRPG if it wasn't developed in Japan. In most cases I find it an annoying question overall, a special bit of navel-gazing.
To that end I would ask if Italian cuisine is still Italian if made by a Swedish chef? The answer is that of course it is, because it isn't about the nationality of the chef, but that the food is made in a style recognized to be in the style of that cuisine.
A JRPG could be made by a team as diverse as imaginable based out of Stockholm, but if it is in the style, it IS a JRPG.
What sets that style apart is a couple key factors in my mind:
Linear Story: The narrative style of JRPGs are closer to that of a film or novel, player choice is minimal to the point of non-existence. You, the player, see the story unfold in a mostly linear fashion and have virtually no impact on the story progression typically.
Predefined Characters: You do not pick what role you will play, you are assigned a character(s). Customization of these characters is limited, typically minor variations with a set class if anything.
That is it really to me, every other aspect you might see argued as a JRPG trope are not really inherent to every JRPG, but the above generally is. (Exceptions tend to prove the rule.)
Turn-Based combat? Well aside from the progenitor of the whole rpg genre being turn-based, you also have examples like Secret of Mana. Because the root of the genre is turn based, it cannot really be argued as a unique JRPG trait.
Random Battles: More pronounced in the sub-genre, but also present in the source genre. (random encounter tables.) Same as the above.
Wild Character Designs? The aesthetic isn't isolated to JRPGs, nor is the game dependent on it.
Summons? Not unique to JRPGs, and though they do tend to be more exaggerated, it isn't as consistent across the sub-genre.
Cecil!? It should also be noted certain studios have their own styles, and that shouldn't be taken as true across the wider genre.
So thats my .02 cents on the issue, how about the rest of you, agree or disagree with my assessment/definition of the sub-genre?