Learning a language and speaking the language of love is completely different.
While Learning a language helps you to communicate well with people across the world, Love helps you to mingle with them. The meaning of "love is an international language" is that love is appreciated the same way throughout the world.
But to express your love, you still need to communicate. Learning a language helps you do it better.
CORRECTION IN QUESTION : My question is talking about the reason to improve the ability to speak a language when we often say that Love is an international language