I started studying English at the age of 9 or 10. Went to an English course. Back then we only started learning English in Junior High School (13 years old). Continued studying English at uni (4 years) and then I started tutoring kids and translating books from English to Indonesian until the age of 28.
Moved to Finland in 2007, started studying Finnish on my own for about 9 months, then went on a full-time Finnish course for 4 months and self-study continues until now.
I use Indonesian and Sundanese mainly with my family through Skype calls and in Facebook with my Indo friends. I rarely use long sentences purely in Sundanese, so most of the time Sundanese words are used in Indonesian sentences to describe things that can't be described better by using Indonesian terms/words. I use English mainly in my blogs and FB and my online activities. I use English verbally with hubby, because when I used Finnish with him, my English pronunciation becomes so weird (Finnish has a similar pronunciation with Indonesian language). So these days I use Finnish with hubby's family and at work and in FB with coworkers/Finnish people in my FB.
My skill levels on those languages have declined in some ways. True, I speak more Finnish these days due to my work, but I'm less concerned with the grammar because most people use the informal version of the language anyway, so bye bye grammar to a certain degree!
Hubby says that I have talked in my dreams using English, Finnish, and Indonesian (he guessed it was Indonesian when he couldn't decipher what I was babbling about in my sleep).
Now let me give you examples of the mess:
1. Every now and then I blurt out an Indonesian word either at work or at home. I have NO idea why!
2. Sometimes I think in English, Indonesian, and Finnish respectively on separate occasions. For example, while writing this post, I think merely in English.
3. Sometimes when I start to think in English (for example), I forget one word and have a hard time finding it on my own. Instead, all I have in my brain is the Finnish or Indonesian word or both Finnish and Indonesian word instead.
4. Sometimes when I speak to hubby in English, I have a hard time finding one word, so to make it easier, I use the Finnish word instead. Not good, I know.
5. Sometimes I try to write an email in Indonesian and then get stuck with one word. I only have the English and Finnish version of the word in my head and the image of the word. Nice! Not!
6. Because both Finnish and Indonesian only have one word for "he/she", my brain has reverted back to its Indonesian root. These days when I talk to hubby in English, I mix up the use of "he/she", "him/her", "his/hers" because in both Finnish and Indonesian, it doesn't matter either way.
7. Sometimes at work when I've just finished serving a tourist in English, my brain forgets to switch back ASAP to Finnish. So, I end up using English to serve the Finnish customer behind the tourist, which usually makes us both laugh. :-D
8. There are times when I start stringing up a sentence in my head in English, but all of a sudden in the middle of the sentence a Finnish word appears.
9. I've started getting more and more confused about English grammar, because my brain sometimes automatically tries to use the Finnish structure of the sentence instead of the English one.
10. I start to get more confused with the new slang words that my fellow Indonesians use. I have no idea what they mean and it's hard to catch up with the new development when I'm not using it daily (well, not verbally anyway). I wonder how much further away I feel the mental distance between me and my mother tongue the longer I stay here.
That said, don't wonder why my English has become kinda quirky these days compared to the old days when I didn't know/use Finnish too much. Has anyone else experienced similar problems?
Note: Apparently they have a term for this kind of phenomena. It's called Language Attrition. It can happen to your mother tongue as well as any other foreign language that you've studied.