There is a lot of variation in article growth rate among mature Wikipedias. Growth slows down at some, is steady or even accelerates at others. Many have tried to model these trends. I have little to offer in explanation but can offer an at a glance overview of article growth trends for top wikis. You can switch between small and large charts, and either look at growth trends alone or match those visually with overall editor activity per wiki.
These charts existed for a while, via wikistats portal you can find similar charts for all other wikis. Navigate to sitemap pages, e.g. for wikipedia, click link Summary for any wiki. More links at bottom of sitemap to grouped summary pages per project.
New: trends are now broken down by type of editor: registered editors, anonymous editors, bots.
Manual article growth has been slowing down on English Wikipedia from 2007, but seems to stabilize in last two years.
Growth in articles on German, French, Italian, and Polish articles has been pretty stable for many years.
Usually spikes in editor activity are caused by bots. A few charts show spikes in article creation rate for registered users. My hunch is these are anomalies, caused by bots not being recognized by name (roughly meaning they do not contain ‘bot’ in name) and not being registered as bot either (which I believe on many wikis is mandatory).
Any feedback on bots that fall in this category is very welcome. If some of these bots are registered after all, next month of charts will reflect this, for all history. Likely candidates for mis-attribution are Spanish spike in 2011, Chinese in 2012, Vietnamese in 2011/2012, Norwegian in 2008, Czech in 2010.
One particular issue prompted this overview, so let me ask: growth in new articles on the Portuguese Wikipedia dropped significantly early in 2011 (it seems to pick up again recently). The number of active editors did not change much in recent years. Any thoughts on this in general? Also it seems counting methodology changed (not on wikistats), or at least was questioned, in March, according to this discussion (Google translates anexos as attachments (?))
Thanks in advance for any insights into these trends.
Upd: for further analysis you can download data files (csv)