Let's examine one of the great classic problems in linguistics: Yoda. And how he talks.
Yoda? Know him you do, surely. The great Jedi master he is! The little green Jedi master he also is. And speak in backwards sentences he does.
OK, that last statement isn't really true. The sentences aren't completely backwards. He doesn't say "Him to you take will I"; he says "Take you to him I will." What's more, not all his sentences are like this. Actually only about half are, depending on the movie; the rest are in normal English word order.
What language does Yoda speak? The answer to this is surprisingly clear: It's English (duh). In all five of the movies he's in, he speaks only English. This is not to say that he doesn't speak any other language, but we actually don't have any evidence he does. He could be a monolingual speaker of the kind of English he speaks. There are dialects of English that are more different from the Queen's English than Yoda's is.
What's more, if Yoda's native language is not English, we can't infer any details of it from how he speaks English. The fact that he shows a stylistic quirk in English doesn't mean that he brought it over from another language. He may have, but he may just like the structure of that way of speaking. After all, he only sometimes uses the "reversed" word order — which means when he does, he probably does it by choice. He could easily have picked it up from English. After all, the people who wrote him did.
Let's look at a few characteristic sentences of Yoda English:
Nothing more will I teach you today.
Size matters not.
Anger, fear, aggression; the dark side of the Force are they.
If once you start down the dark path, forever will it dominate your destiny, consume you it will, as it did Obi-Wan's apprentice.
For 800 years have I trained Jedi. My own counsel will I keep on who is to be trained!
Much to learn you still have.
When 900 years old you reach, look as good you will not.
Lost a planet Master Obi-Wan has.
Now let's look at some bits of English that do not come from Yoda, but sound like they could have:
Round about the cauldron go; in the poison entrails throw.
Else the Puck a liar call.
For them the gracious Duncan have I murdered.
I like him not.
Come, they told me, the newborn king to see.
Ever-returning spring, trinity sure to me you bring.
Of your father I won't even speak.
The first four are from Shakespeare. The fifth is from a well-known Christmas song (with "pa-rum-pa-pum-pum" removed; thanks to Arnold Zwicky for that example). The sixth is from Walt Whitman. The last is from The Apprenticeship of Duddy Kravitz by Mordecai Richler, and it shows a characteristic turn of phrase in Yiddish-influenced English.
These sentences remind us of Yoda-style things we can do in poetry and other stylized forms. We can put not at the end ("I like him not") rather than attach it to the auxiliary do ("I don't like him"); this used to be standard English. We can move the verb to before the subject ("Duncan have I murdered"). We can put the conjugated verb at the end — which was standard in dependent clauses in Old English (and still is in German). And most importantly, we can bring stuff from the end to the front, as Yoda does.
When you bring a later part of the sentence to the beginning, it's called fronting. You can front just a noun or prepositional phrase — "Jackets we hang here, ties we pile over there"; "The life of Riley, you live"; "For $5 you came here?" — or you can front a verb with it as well, as long as you keep a conjugated verb (such as an auxiliary do or have or will) at the end — "Likes it hot, he does"; "Park in my spot, will he?" Sometimes we even leave off the verb at the end, when we start with a shortened sentence and then clarify: "Makes a lot of money, your friend?"
Why do we front things? To put key information first. Perfunctory bits can wait till the end. Perhaps when 900 years old you are, do this you will also, as dead you may be before finish the sentence you will. Going with this, Yoda typically keeps the conjugated verb at the end — maybe because 900 years ago that's what we normally did in subordinate clauses in English — and puts the not at the end — because, again, it's old-style and more direct.
And why not? What would you do if you wanted something that sounds a little quirky and exotic and appropriate to a wise Jedi master who happens to be a two-foot-high green gremlin-like creature with the voice of Miss Piggy? Why not draw on archaic and poetic forms, and also on colloquial forms and some turns of phrase associated with Yiddish-influenced English, which is stereotyped as knowing and witty?
Because remember: Yoda didn't write his own lines. He is a character in five movies written by several different screenwriters. In Yoda-Speak: A Study of Yoda's Speaking Patterns and Their Frequencies, Michael Kaminsky gives a detailed run-down of how Yoda's speech varies from movie to movie — and screenwriter to screenwriter. So you have different versions of Yoda's speech; sometimes, for instance, the pronoun comes before the verb ("Received a coded message we have"), sometimes after ("Heard from no one have we"). But somehow they all manage to adhere more or less to a recognizable, comprehensible style.
And that's the thing about Yoda-speak: We understand it. It is comprehensible English because it is written by English speakers, for English speakers, using things you can do in English. If we were to put the words in the order you'll get them in even some of English's closest neighbor languages, it would be much stranger and harder to understand:
Is planet lost at Master Obi-Wan. (Gaelic)
I not you will-teach more today. (French)
I will my own counsel on them, who trained become, keep. (German)
In some other languages, you couldn't even do word-for-word — you might get just one or two words with a lot of prefixes and suffixes. And in extraterrestrial languages? All bets are off.
But Yoda speaks English.