What should I know about rift before buying it?
And what things should I know in the game not to be a noob lol (rift vocab/slang)

There are 4 classes consisting of mage, rouge, warrior and cleric.

Each class has 9 souls (so 36 in total), souls are mainly skill trees. You can use up to 3 soul (skill) trees at a time and you can mix and match as you please.

There are 10 professions which can each be leveled to 300, you may only have 3 on a character at any given time. Getting rid of a profession means you'll loose all levels in it and be reset to 1 of 300 if you pick it up again.

Just google anything else you need to know...

I bought it last week and I'm having fun with it. until you get to about 20~ it'll feel pretty much like any typical mmo, but when rifts actually start to get interesting and you can start assisting in the world events, it definitely becomes something more.

I'm not sure how intensive the end game is, and there are far less zones than for example, in wow, but the zones are large and there are plenty of quests to get you through them.
you have no repair bills, arrows, or any menial bullshit to deal with, which is extremely nice. the respec cost is far less than what you paid in wow, (sorry for all the wow comparisons, only other mmo I really got heavily into) both resurrection and travel systems are greatly improved over wows as well.

that's about all I've got for now, but like I said I'm enjoying it, much worse ways I could be spending my time.

Biggest pieces of advice I can give if you pick up Rift:

1. Do NOT be afraid to multi class... It helps you more than you can imagine. Helps you get in more dungeons, be more versatile in any situation, and helps you further understand and appreciate the different roles quickly.

2. Respec if you have the slightest curiosity/incline to. It's cheap to do, fun, and generally gainful to do this. The game being so young, I dare say a lot of the "recommended" and pre-builds you find online may be effective, but every person has their own way about playing. Those builds might need a bit more tweaking to fit your needs.

3. If you're like me, or anyone who likes to be as utilitarian as possible. It's annoying at first (no feel of gain), but make your first toon all 3 gathering skills. Second toon armor OR weapon smith, runecrafting, outfitter. Your second toon will be a powerhouse crafter once everything is set up and running. Runecrafting will feed off of outfitter, and armor/weaponsmith purples will feed off of runebreaking. Keep in mind, the mats gained from runebreaking will be easiest gathered once second toon is 50. They are gathered from purple item drops.

4. Your concerns with lingo... Majority of the terms are the same used in WoW (from what I've seen/heard, never played WoW personally). There are plenty of people who don't hesitate to answer the "noob" questions on terminology in game though. Surprisingly friendly (personal testimony from my server and faction, no guarantee for all of them though lol)

5. There are minor glitches here and there that you'll stumble upon, easy to report and they seem quick to patch majority of issues reported.

Dunno if any of that helps at all, hope it does.