Should I learn two languages at once?
We get this question a lot.
And it's a difficult one to answer. Surely it's possible, but I know that in my personal case, trying this has always been a disaster.
Now, when setting off on a new journey of learning — or any new venture, for that matter — I try to remember to F.O.C.U.S.
In other words, if learning Japanese is not a priority, then you're going to have a very hard time getting through the four phases to near-native fluency.
I do think that maintaining the progress you have achieved in one language while trying to improve your abilities in another is feasible, however.
If someone told you, "Go through 150 NativShark units in the next 10 days, and we'll give you 1 billion dollars" ...yeah, you'd probably make it happen.
In the process of making it happen, though, some other priorities would fall to the wayside, yeah? You certainly wouldn't have time for work or school, for socializing or relaxing. Instead, you would have to be so laser-focused that nothing would come between you and the accomplishment of your life-or-death goal.
Life's not that simple, but it can help to think about that analogy from time to time.
By definition, not everything can be a priority. Focus is critical.
At the end of the day, only you can decide if learning two languages at once is practical. If you can make both languages a higher priority than some other things in your life, then theoretically it is feasible to learn two languages simultaneously.