Recently back to WoW

[Mereinid]

I have just returned back to wow, less than a week now. I see a huge amount of changes have happened..however I am not finding any info on the general make up of wow on the back-end?
Did Blizzard change the way WoW handles UI mods now? As I have downloaded quite a few *updated* mods. Ones that have come out in the past week or so. All I get is UI errors now and the only thing that stops them is for them me to completely disable all mods and play with a virgin UI. I take that back, the only mods I have been able to get to work with out causing some error is a graph paper one and perl Unit frames. Mail, Quest, Action bars and bag mods have all repeatedly been popping up errors and one called a pet journal. My main is a rogue and I done even have a pet, not even a vanity pet out. Bartender worked for about a day and now, as of an hour ago, has stopped working.

I apologize if this has been answered in some form or another. I never had anywhere near this kind of issues this past year 2013, before I left the game. I basically was just wondering if they have an all new User Interface language or not supporting any kind of mods now?

Thanks for your time everyone, luck and loot.

Regards,
Mereinid