I'm stuck on the more interesting problem of why a President would need to be a linguist, but in general I don't see the point of worrying about it if your character fits the role and is relatable (doesn't have to be in a good way).
I don't know how useful those litmus tests are. I think one of the most determining aspects will be how he fits into the story. It's hard to gauge characters that exist in vacuums. It's not enough to have a deeper character, you need your plot to bring out his characteristics in a believable way.
From what you described, it sounds like you have a good base to work with. Have you written any of the first draft yet? If you haven't gotten far, doing so should help you figure out what, if anything, will need to be re-evaluated about this guy.
"He's not all totally bad because that would be very 2d"
I disagree with that statement. You can have "totally bad" guys that are "3D". Think of heroes; if they were made straight from the definition, they'd be "2D", too. However, when you give them cause to be who they are, that adds the third dimension. Same thing can go for the villains.
Meanwhile, the gist of Mary Sues/Gary Stus is that they're generally flawless and everyone in the story is oddly okay with that. Your guy sounds like a total bastard--and that's a good thing. Sometimes you need bastards in your story. He already sounds adequately developed (eloquent and evil, always a good combination), so I don't think you should worry about him being a Mary Sue/Gary Stu...
So long as: -He maintains his flaws that are actually flaws (not just comedic derp moments like "La dee dah~ *trips down stairs* Lulz, I'm such a klutz") -He makes mistakes -Other people acknowledge his mistakes and flaws -At least someone doesn't like him -That one person who doesn't like him isn't unreasonably hated on by everyone else -and so on.
So long as your character is believable, he should be fine.
Hmm... sounds more like a Byronic/Antihero to me. He has some serious flaws to outset his skills as a leader.
I wouldn't trust Litmus tests though. I came out with a higher number on the list, but due to the nature of my character's occupation as a Marine in a science fiction setting, it's acceptable if some things like knowing more languages or being able to familiarize himself with any weapon or environment is acceptable, plus as long as you have flaws that make them a believable person, then it ain't a sue.
There are smart people in the world, and Mary Sue is a commonly tossed about term that sometimes loses its meaning. I would actually agree with neomerlin's response and have people actually analyze your character. With proper feedback, you should be able to come to a concise conclusion!
I... I think I knew, once upon a time, what a Mary Sue is supposed to be. But honestly, I just don't know anymore. It gets used so much and applied in so many ways it seems to have become entirely meaningless. So is your character a Mary Sue? The answer is flurgaboot.
Is your character good? Will people like reading about him? Is he well defined and well rounded? Does he seem like he might be a real person? Do his actions and his reactions make any kind of logical sense? These are important questions but I can't answer them. It's one thing to read about a character in a story but I can't judge how the character has been written without reading the story the character is in.
My advice to you, if you want feedback on the character, is to write the story and then get some reader feedback. Some people have what they call "beta readers" to help them when they're writing something new and editing it. But before anybody can judge the character, you need to write the story. If you're honest with yourself, you'll probably be the first person to know if there's something very wrong with how the character is written. And if you're having doubts, then it's time to go back to the drawing board and do some improving.
I was thinking on making him not be redeemed, mainly because he's murdered poeple haha and he's a little sadistic. He's not the kind of 'look at me, gah im so misunderstood, nobody loves me, cry cry cry' and he finds happiness in the end. Its more down the route of 'shit happened in my past, and I'm a fuck up now, but that doesn't excuse the terrible shit I do'. He's not just a bastard, he's literally probably a sociopath. There is definitely a big plot behind all of it.