Simple Pie example

SimplePie.java

@Override
public void onEnable() {
    Metrics metrics = new Metrics(this);
    metrics.addCustomChart(new SimplePie("used_language", () -> {
        return getConfig.getString("language", "en");
    }));
}
// If you use the Copy & Paste Metrics classes, use `Metrics.SimplePie` instead

This example should be simplified as (at least) Java 8 supports simpler Lambda expressions.
E.g.

@Override
public void onEnable() {
    Metrics metrics = new Metrics(this);
    metrics.addCustomChart(new Metrics.SimplePie("used_language", () -> {
        return getConfig.getString("language", "en");
    }));
}

getConfig should probably be changed to getConfig()