Migrating from Gitbook

I am trying to migrate some docs from Gitbook and being brand new to VuePres I am unsure of how to do something. We have these conditionals in our docs that are used for 2 purposes. When we are running the documentation in dev mode (gitbook serve) they only show 1 language. The more important piece is that when we build it we build documentation for a specific language. That means where ever we see these conditionals they need to be evaluated, only show one language and build it into that languages folder (java/.net/etc)

{% if book.language === "Java" %}
    int numOfBananas = ...;
    String message = 
        "We have " + numOfBananas + " banana" + (numOfBananas != 1 ? "s" : "");
{% elif book.language === 'C#' %}
    int numOfBananas = ...;
    string message = 
        "We have " + numOfBananas + " banana" + (numOfBananas != 1 ? "s" : "");
{% endif %}

I know I can use vue directives and logic in my markdown files but what I am unsure how to do is pass additional options to vuepress dev and vuepress build and where to store those options. Any help here would be greatly appreciated.