It seems that the skill of translation can be quite separate from the ability to communicate freely in a language. My son took a standardized test given to all students in our prefecture the other day, with an unexpected result: he got a relatively low score on the English portion of the test. This surprised us, considering he's fluent enough to watch American TV and movies without even paying close attention to the screen, and only occasionally has to ask me what certain specialized words mean. The test called on the students to translate sentences from English to Japanese and vice-versa, which seemed to present a special challenge for him because of the "raw" way he learned English, talking with me, interacting with his family in San Diego, and learning from native teachers at the experimental English school he attends. Because I learned Japanese as an adult, "connecting" the vocabulary and grammar to concepts already in my brain, I can think of a Japanese word like mezurashii (meh-zoo-rah-shee) and the English meaning (unusual, rare) will spring into my mind. But in my son, the synaptic bridge joining these two concepts might not have been created yet, potentially causing interesting difficulties in moving meaning from one language to the other. If you want to learn about how your own brain works, study a foreign language!
The act of learning is actually creating synapses in your brain. Isn't that freaky?