Learn concepts, obtain foundational computer science knowledge, write complex projects
not just get familiar with somebody's interpretations that they implemented as a language.
Languages that I used besides my job language barely gave me anything, in most cases they made me appreciate more for sane environment (package managers, IDEs, debuggers, strong standard library)
edit. just to be clear:
I don't see value in learning C#+Java+PHP, but C#+Erlang? yea
I do see value in learning Rust after C
but still - concepts are more important, you don't have to learn langs in order to be familiar with concepts
Learn software engineering - it's broad as hell and you can easily do that using one language