I can't comment much on LoL, since all I know about that game is from hearsay and the odd "LoL player switching to Dota" thread on the Dota 2 subreddit. I have heard that it's fairly common to "main" a hero or role in LoL, which I don't suggest doing on Dota. You should really be prepared to fill in any role. While Carry and Mid are the most popular pub roles ("Mid" not really being a proper role, but it's called early very often), I have ended up on all-support teams. I learned Dota by randoming constantly, and I really feel it served me well. I quickly developed a very good understanding of each hero's mechanics, while some of my friends who got into the game at the same time took much longer. And that understanding is just as crucial for playing against those heroes as it is actually playing them yourself.
On turn-rate, which I saw mentioned: Yes, it is an actual mechanic in Dota. Some heroes have very fast turn-rates (like Bristleback, who takes reduced damaged when his side or back is facing the source of damage) and others have slow turn-rates (like Elder Titan). A few heroes have abilities which can affect the turn-rate of enemy heroes (Medusa, Batrider). It's just another thing that adds to the depth of the game.
As for the "Russian" and overall community issue: It's an online community. You should know what to expect by now. Yes, you'll run into a fair share of foreign players. Don't prejudge them, though. I've met many who were actually able of speaking great English and were competent players. And if anyone does bother you, mute them. Simple as that. You can report them as well. On the whole, though, I'd say your best experience will be partying up with friends. I'm usually in Ventrilo with 3-4 friends while I play, so random pubs aren't a problem as often. If you don't have that luxury, then look for opportunities to find people to play with. There are in-game chat channels where you can meet people, there are forums (Giant Bomb comes to mind. The Dota 2 subreddit as well, of course) with robust Dota communities where people are often looking for others to play with. And if you meet someone you enjoyed playing with in a game, send them a friend request. With very little effort, you can improve your experience with the community greatly.
Also, the game is very deep. There are tons of mechanics that aren't readily apparent, and knowing these will make you a better player. However, don't let this overwhelm or discourage you. Remember that you're being queued up with people on a similar skill level as you, and you're not likely to find any newbie players (maybe the odd scrub account, etc) who have a good knowledge of many of the game's mechanics. You can learn these on the fly, and will be perfectly fine doing so.
If you DO want to learn more, then there's a wealth of resources. I love watching Twitch streams (Draskyl, Blitz, Purge, Merlini. The latter two also have Youtube channels that are great for learning, as they explain a good bit while they play). The Dota 2 subreddit does regular hero discussions, which are great for learning nuances of those heroes. Dotafire.com has some awesome guides as well. There's also a series on Youtube for absolute beginners called "Dota for Dummies". Try looking it up. Like I said, you don't NEED all that knowledge at the start. But the resources for learning it is readily available.
