I think that if you learn a language well enough, deep enough that you can commune with it's native speakers on a level similar to your mother tongue then your character will completely change depending on who you are talking with. Different languages offer you various ways of expressing yourself, ways that other languages perhaps may not (culture too). It's only natural that you change your mind frame once you change the language coming out of your mouth. When I speak Japanese I feel myself being overly polite. When I speak Chinese I feel professional and easy to get along with my peers. When I speak English I feel most natural and confident in myself. Each scenario brings out a different me!

Hello Xiaoguiren It would certainly widen your horizon , enrich your life experience , but it is not the language itself ,rather mingling with its native speakers and picking up some of their habits and ways of conduct Imagine you just learned the language on your own using some tools like books , cds and a non native speaking teacher , you will certainly not be influenced as much as you mingle with natives .So it is the culture , the tradition and heritage of the language that effects one and it depends how deep the person indulges in that culture . If you live in the country where you learn its native language you are more likely to change your attitude, simply because you are mingling with all aspects of life there , less and less if you are just learning the language in your own country of residence .

Very good question. I think Richard's answer is pretty insightful. I would add, similar to Jura, that character is something that is somewhat fixed, at least once you become an adult. So I would not argue that one's character changes depending on the language spoken. However, I would argue that the PERCEPTION of one's personality by others is changed a lot by the particular language. An example. One of my very good friends was born in Taiwan, but raised in the US. By any measure, his English was as proficient as mine. I always thought he was a shy person, because he didn't talk much until you got to know him. He and I have since moved to Taiwan, and here, this guy is extremely outgoing, a real networker. I almost couldn't believe it was the same guy that I knew from the US. Bottom line, he wasn't a shy person (his true character). But a lot of people "thought" when he was in an all English environment.

I have learnt 4 languages & now I'm learning Italian. Whilst my knowledge of different cultures & traditions has broadened my outlook on life, personally I don't think that it's changed my character.

if you speak formal Bahasa Indonesia, you will feel like alien. because native speakers always use the slang word, and the formal is only spoken ocasionally. and if you try to use the slang words, you will feel like not speaking bahasa indonesia at all ! in conclusion, yes i think learning foreign language will change your character but only by the time you're using it.