The best approach at this point is to clone one of the existing plugins. The first question is to ask "what kind of plugin?" Adding functions to Gnumeric? -- take, for example, fn-math Adding a solver method? -- take glpk (external program) or nlsolve (internal). Anything else? samples are getting a bit thin.
OK, thanks.
How is integration set up for other programming languages (e.g. Python): through the plugin API?