Im wondering if there any legit way to choose the order of your buff, cause when im in group i cant see my convention of the elements buff.

Nope. We're fucked until they fix it, albeit a couple years late.

if you learn to look at your character well, you can tell which element you are on from that. At least for most elements its obvious by color.
Otherwise no, sorry.

you can use this website to help you out:

http://awsmsauce.net/

nope

buuuuuuuullshiiiit

have you ever looked at your character with a COE equipped? Theres little circling guys that change color. You can't tell electric from cold, but you can tell arcane from cold/electric, fire, etc.

Not practical at all.

Too many other shits to look out for.

depends on your class and build. Its easy enough to look at when you're a barb or something. Much harder with wizard or monk, they have flashier shit. I'm saying its possible, but usually not that useful. Its about as much work/distraction as going and looking for the indicator in the buff list which is what OP asked about.

The list caps out and you can't see it at all. It's not about searching for it.

You can't see the convention on your character at all in group play, it's not a viable method. The only way to get it is to use a third party program that shows you all your icons, or shows the convention buff elsewhere.