Conclusion, it did not make a dent. Most people dismissed the banners, and never clicked, those that did, never followed to edit. It made little to no difference in the visitor or editor stats for the period.
Theo,
Clearly, links in sidebars are not getting enough eyeballs. It is also hard to look for one's own language when there are too many interwiki links. Unless you are intentionally looking for it, it is hard to notice.
What I am suggesting is a country specific clear navigational aid which is a best practice that all major websites follow (WordPress, Google, Facebook all show Indic language version links if I access from India.
It will be interesting to analyze why the banners did not work. If we are inviting people to contribute, only people who would like to contribute may check. The behavior may be different when we try different messages. Also, I am not looking to convert people to editors. Merely getting more readers and increasing awareness about the existence of local language versions is a great win.