I had always taught that Japanese normally say "watashi wa anata o aishitemasu" whenever they want to express love to someone. But when I learned about Japanese language and culture, I discovered that such is not the case.
The expression "watashi wa anata o aishitemasu", which I first learned from Leah Navarro's song "Isang Mundo, Isang Awit", is indeed a correct translation of the English expression "I love you", but it is rarely used by Japanese. There are several reasons to this and I will try to discuss them below.