I did some further analysis from which I would like to group the projects into the following four cathegories.
Have had exponential growth, but plateaued about three years ago: en,ja,de,es,fr,it,pl,pt,nl,zh,tr,sv,fi,cs,id,he,no,da,sk,el
Are in exponential growth phase: ru,ar,vi,ko,ro,uk,fa
Has grown linearly, and is growing linearly: hu,hr,bg,ca
Ambiguous. Most seems to have been at a plateaue since the data I used started being collected: lt,eo,sl,ms,sr,et,simple,eu,bs,ka,gl,hi,mk,cy,te,nn,lv,ml,br,af,la,mr,ta,bn,tl,az,zh_yue,is,sq,be,sh,lb,an,be_x_old
The first two classes seems healthy to me, and shows growth that can be expected. If we want to do better we can however ask what can be done to rise the plateaue level. The third class does also show growth, which is good. But I think a realy healthy growth should show a period of exponential growth, so this class might be a problem class. The bigest problem as i see it is the fourth class that seems to have been stuck at a low level (these projects has a couple of hundred active editors or less), and for many of these projects I think there is opportunity for exponential growth. But what are the problems that has not made them grow?
For the languages I havn't included in this analysis there is a lack of data, but most of them (if not all) is doing worse than those in the fourth class. So these do all belong to the problem class as well.