Probably you should consider
learning .NET[
^] framework;
C# as language[
^]. It would be fun programming .NET applications. To be noted, these are high-level languages. Since you've already learnt JavaScript,
learning Java[
^] would also benefit you... For
programming Android applications[
^].
For low-level language, you should consider
C++ to be learnt[
^] and other languages might include
SQL[
^] (for databases).