Someday, I would like to say that I know one foreign language inside out, speak several (3-5) to a high degree of fluency in a manner that isn't too far off from native pronunciation, with knowledge and some understanding of many others.
Deep understanding matters somewhat and in some situations, but not at the cost of a good enough or even very good understanding of more languages. Specialization is overrated. Being a polymath is much more appealing to me.
"A jack of all trades is a master of none, but oftentimes better than a master of one."