1. I can tell you, as a student of linguistics, that languages differ not only in what words they use to describe things, but also how they sound. In other words, all languages have rhythm. To the western ear, japanese and chinese might sound like the same gobbledygook, but if one listened closely, one would perceive the musicality of these two languages, so much so that, even if you couldn't speak either of the two, you would be able to distinguish one from the other. Am I suggesting that it's not we who change personality between languages, but that it's the languages themselves who have personalities of their own? Kinda. Historically, we tended to associate certain languages with certain human traits: german is the language of hate, french is the language of love, etc. 2. Native speakers have certain anchor expressions (not a technical term) in their speech. Terms that link parts of the sentece together. Like uhm or like, for english. "And, uhm, we just went there."
"She was, like, completely disgusting." Generally, english-as-a-second-language speakers tend not to use those. It's not something that can be taught. You learn it by hearing other people use it. So, perhaps, I'm speculating, your confidence and security may come from the absence of these little words. They increase the fluidity (again, not a technical term) of speech, so their absence may increase the seriousness and gravity of it.
Do you think that there is any validity to the "performance" aspect? If you are speaking in another language, perhaps it gives you the ability to hit the "reset" button on who you are and start over. If you are normally considered to be a sheepish person in your native tongue, perhaps speaking in another language gives you the opportunity to "perform" differently? I can speak some spanish and I tend to be a bit more "suave" when speaking it. Why? I think it's a bit of what you say, the language itself has some pre-conceived traits, but I certainly embellish these traits. I'm a bit more passionate in spanish than I am in english. Plus, it's just really fun to speak.
I think I have to agree with you on your first point. Personally I speak Dutch and English (and a little bit of German and French, as every Dutchman), but I feel differences between Dutch, English and German, even though all three of them are Germanic languages (yes, I left French out) English is more polite (at least British English is) than Dutch and German is harsher. I know for a fact that my nephew, who lives in Germany, sounds completely different when he speaks German, even if he is saying the exact same thing. As for the second point, words like uhm and like are present in pretty much every language, but I personally don't find that they improve the conversation, they only hamper it. These words are mostly used if you do not know what you want to say or when you do not know which word you need. I agree that these "anchor expressions" are present, but I disagree with your speculation that they would increase the fluidity of the conversation. What I would like to add is that in when you converse in your native language, you use small jokes and wordplays (just pay attention). These small jokes and wordplays lighten up the conversation and make is seem less serious. I think that the absence of these jokes when you speak in another language might also add to the seriousness of the conversation.
My wife often laments this. Her native tongue is Chinese, and she likes to make people laugh. When I watch her speak Chinese, she uses a lot more witticisms. She has said that she feels she can't be her whole self speaking English, especially when multiple people are conversing and it's moving fast.What I would like to add is that in when you converse in your native language, you use small jokes and wordplays (just pay attention). These small jokes and wordplays lighten up the conversation and make is seem less serious. I think that the absence of these jokes when you speak in another language might also add to the seriousness of the conversation.
You're absolutely correct. Some much that they're called speech disfluencies.