We usually advise that it is best to learn one language at a time. The reason for this is that (new) languages have a habit of getting mixed up in our brains, even if the two languages are quite different. So you end up spending time trying to keep them straight and therefore making less progress with the actual learning part; when instead all of your efforts could go towards one (new) language. Learning one at a time, therefore, typically results in better and faster progress.
Of course, there are always people who are exceptions to the "rule," but this would be our advice.