Spanish is my mother language. I can understand catalan, because when I was a child I watched TV programs in catalan, and I eventually got to understand good part of the most common expressions. However, I have never had the chance to speak it.
Then, I learned a lot of english since I got internet access, in chats and contacting natives I got to learn a lot of not-in-the-textbook english, and learned to express myself better and be more fluent. That is however for the written part, pronunciation is still very hard for me to get right.
In high school I chose latin and classical greek, which gave me a better understanding of differences between languages, and the way occidental languages developed. Currently I can also read modern greek, despite I can only imagine the meaning of some of the words.
I began studying japanese on my own when I was in high-school, using books, references, and attending private lessons. When I got to use it a little bit more, I began making friends with japanese people studying in Spain, and I managed to improve my conversation and learned a lot of expressions in japanese. Currently I am living in Kobe for 4 years, so I can speak it fluently, and even recognise and use dialectal expressions.
In university I majored in italian, choosing latin as secondary language. (actually I chose german first, but it was too hard for me, so I switched!

) I can understand and use italian, although not in an advanced level.
So, in order of performance level, it would be spanish, japanese, english and italian. I have been fascinated by languages since I was a child. For example, there is a series of products that come packaged in 3 or more languages so that they can be used for different european countries. I always readed what was written on the biscuit boxes in protuguese and french, and tried to figure out the meaning by contrasting with the text in spanish
I also find alphabets very interesting, just yesterday I learned the corean alphabet, which is amazing.
Here are some interesting links, but I'm sure many of you will already know them:
Word Reference: dictionary in italian, spanish, english, french, portuguese. It has utilities such as definitions dictionary, synonims dictionary and forums where to ask for doubts.
Jim Breen's japanese dictionary: when looking for words between non-related languages it's not such an easy task. This dictionary is helpful when you have are studying japanese and have a certain degree of knowledge.
Omniglot: a page about writing systems and languages around the world. It even includes science fiction alphabets, such as star wars or alien nation.