Are track lighting systems standardized/universal?
No.  First as you have mentioned there is line and low voltage.  If you are not sure what to choose from pick line voltage - you can always put it on a dimmer to get what you need.  The low voltage tracks in my opinion are junk because they only allow a certain amount of light, and the transformers go out or hummmm after a while.  That is just my opinion on this - people will say you can find more selection of light bulbs with low voltage and there are special circumstances where this is right but you can order a lot of stuff easy on the internet now.

OK back to your main question.  No again.  In the US there are three main types.  See the picture below.



Get a ladder and take a look at your track or take a picture on your phone.  The Juno tracks I have seen have been j-style but you need to look because they are a huge maker and I am sure they have made each style.