dh is fluent in english, but is dutch.
When we married we moved to Holland so I could learn dutch, and as soon as I had the basics, we switched from english with friends and family to dutch. I remember being amazed at the personality changes I saw. I knew all these people well through eng lish, and they spoke english well, but in their own language they were very different.
I think your language can change your perception. My mum and I were talking about this this morning. I lived in Indonesia, and while they have words (mostly imported words) for lots of colours, they only use a very limited range. So a dark purple colour is described as blue or red, and they would never use the word for purple. One of the common colour words that they use is red which covers any colour from pink, through orange to red and then burgundy. This isn't just a language use thing, they don't discriminate between colour in the same way we do. If asked if two colours are the same, they are much more likely to say they are than we are, and I think that is to do with language, we have 30 words for colours, so we divide colours, and see differences between them.
There is also a close link between language and culture. I never knew the actual names of many people as you use their title, (like saying Mr and Mrs but without a name after it) and you use different speech patterns for those 'higher up' than you and for those 'lower down' than you. By the same token, you can signal a lot by a subtle shift of language.
I am different when I speak in different languages, but a lot of that is fitting the cultural pattern, rather than my personality changing.