Haste is your enemy
The modern world is obsessed with a “here-and-now” compulsion which is particularly harmful to language learning. It is no wonder that in Italian, as well as in many other languages, a long series of proverbs exist on the pernicious effects that haste has on our lives. For example, “Haste is a bad counselor,” “Slow and steady wins the race,” and so on. The first six months of the learning process are the most delicate, and one needs to focus on a given language daily and dedicate to it quality work. Time is a luxury that modern men lack, so if you split it between two, three, or even four different activities, the quality of your learning will suffer. Therefore, I personally recommend learning one language at a time.