Well?
Yes.
Oh, did you want more answer than that?
Not all that much. My native language is Dutch, and I learned English from movies and messageboards. I often find myself thinking in English. However, that doesn’t mean that my personality has somehow changed, or that the way I think is tremendously different. For me, it’s just like having an extra large vocabulary at hand.
YMMV and all that.
It depends on how much different the language is from your own native tongue and culture.
and how so? I mean apart from just knowing more words.
Which languages do you class as secondary ? 
If we’re being pedantic then I think that learning a second language is different from *speaking * a second language. I wouldn’t say it changes the way you think exactly but studying other languages makes you aware that some “concepts” aren’t written in stone and that there are different ways to look at the world. I think you seldom adopt the “other” way of looking at things but you know it’s there.
For example - there is no translation for “to have” in Welsh, there is simply something “with you”. Now that’s an interesting view of possession.
In English we have this wonderful concept of unfinished or non-specific time “I have lived in Paris.” where most European languages are “limited” to either “past” or “present”.
This is GQ rather than IMHO, however, based on my experience it sure does. Certainly the way I express myself, mannerisms, thinking, etc are different in Chinese or Japanese than when I use English.
maybe I shouldve posted in IMHO instead, I wasn’t really sure where to put. Anyway, mr Chinaguy, could you elaborate on how your thinking is different?
I’ll elaborate.
Yes, it does. I am an English-speaking Canadian, who underwent many, many French classes throughout school. I attended a French Immersion school for grades 5-8, and took an in-depth French language and literature course in high school.
Unfortunately, despite all this, I can very confidently say I don’t speak French… at least, not very well. I can understand it to an extent, especially if spoken slowly and clearly, and I can stumble through the basics if I absolutely must. But that’s about it.
Regardless, there are times when I surprise myself by thinking about something and connecting that something to its FRENCH name first. (I haven’t taken a French course, or spoken French for any significant amount of time, in probably 13-14 years.) I don’t think in French sentences or anything, but I suspect I might if I had kept up with the language.
This could be getting very cloudy. Obviously you have to adapt yourself to the constraints of the language you are speaking and the further away that language is from your mother tongue the more likely you are to be aware of the changes.
I know I am more direct in French (as they are) but I still feel have vestigial anglophone guilt that I might be thought rude - the way I express myself changes but not the way I feel. Having said that I can be as uppity as the next (French)man if someone uses the familiar ‘you’ form with me when I feel they should be showing a tad more respect and you should see my hands fly when I’m speaking Italian 
One of my favorite examples: I was sitting in a laundromat waiting for my clothes to dry & reading some of the informational signs. One of the laundromat rules was, “No Loitering”. There were rules listed in Spanish as well; the translation of that rule was, roughly translated back to English (I don’t remember the exact Spanish words), “If you’re not doing your laundry, stay the hell out.” There is, apparently, no direct Spanish equivalent to the English verb ‘loiter’. And as I thought about that, I realized that that word is a spectacularly vague and virtually useless one; although the Spanish required a considerably longer sentence to express the rule, the Spanish version was considerably clearer about exactly what was being forbidden …
I believe it was Heinlein that said that having a second language is like having a slightly different map of the world and since learning Swedish I can second that opinion.
There are concepts that are different, allowing one to think in a different way, like taking a road that doesn’t appear on your “Standard” map.
And things that can be said in one language but not in another.
Many scientists, Stephen Pinker being one of the foremost amongst them, believe that you don’t actually think in a specific language, and that there is a unique “mental language” from which people translate into speech. Pinker’s book The Language Instinct discusses this at length.
Since learning Spanish and using it on a daily basis, I can say that, “yes,” having learned another language does subtly (at least) change the way I think about things. I don’t mean that I’m not suddently a math wizard or a better engineer, but it really has opened my mind about language origins, grammer, some basic social concepts and assumptions, although some of that could also be a result of exposure to the culture of that language as well.
I definitely do find myself thinking of a concept in Spanish and having no elegant way of expressing the same sentiment in English. Going back the other way, though, I just translate literally and then explain why I said what I said, and observe the understanding grimaces.
Yes, it can change the way you think. There are usually some concepts in the ‘new’ language that your primary language does not have, even if the primary language has some similar or related concepts. If your first language is English, it has borrowed from so many language that it can be hard to appreciate that there are concepts in the other language that English does not have.
Fantasy writer S. H. Elgin did a series (Native Tongue) where the protagonists are linguist women. In it, she gives examples of how a language can lack a word for a particular concept and how a new concept can change the way you think.
The issue isn’t speaking a foreign language, it’s more a question of learning from the culture that is represented by the foreign language.
For example— lets talk about 4-footed ruminants :
think quick!-what do you think of when I write the word: “cowboy”.
Now, to compare: What does an Masai bushman in Africa think when you say the word in his language for “a person who herds cattle.”
The bushman in my example probably is incapable of conceiving the ideas that you thought of. In English, you thought of a Hollywood cliche–the tough, independant, maybe dangerous, man with a gun living on the fringes of society. In his language, the African probably thinks of a wealthy, respected member of his tribe, who keeps cattle as part of his high social status.
Which ones are those?
It’s true than French and Italian don’t make a distinction between the preterit and present perfect (literary French permits the use of the older preterit form, though), but both things can be expressed perfectly well with a bit of context. Plenty of other languages have two distinct forms, just as English does. Spanish, Portuguese, German, and no doubt quite a number of others all have the distinction you describe.
It sounds very much like you are describing one of the early beliefs of linguists that have been thoroughly debunked for decades. English is not unique in borrowing extensively from other languages, nor are there any languages there are significantly more or less “sophisticated” than others. The fact that your language doesn’t have a word for a concept has no bearing on your ability to conceive of, or comprehend, that concept.
If the OP is asking if learning another language changes what you associate with ideas that are presented to you, then the answer is almost certainly ‘yes.’ If, however, the question is, does the process by which you think change if you learn another language, then the answer is almost certainly ‘no.’
Learning Latin helped my written and spoken English immensely.
So the idea of Newspeak ever having had its intended effect is doubleplusungood?
Really, I don’t mean that to be silly – it’s a serious inquiry, I having no awareness of these dubunkings. Newspeak would have, of course, removed so much from the language with no means of expressing an idea, would it be limited to just plot device in the real world?