What language are you currently using and what type of graphs are you looking to create?
I'd recommend sticking with something you know. That way, you don't have to learn a brand-new language from scratch; you can create graphs as quickly and easily as possible. Otherwise, you could probably create graphs with any language, for example, C++, but it would be a major new project.
If you already use Microsoft Excel, why not just import the data to Excel and use some of its graphing capabilities? Or, if you just want a plot of raw data (numbers), you could use a free online tool like Desmos. Otherwise, there are more sophisticated tools available aimed for scientific applications (e.g. Octave, SciLab, etc.)
It all depends what kind of data you are planning to plot, and the type of graph you would like to create.