Mass content adding/Splitting the project
It seems that I didn't read well existing projects on Meta. From 2004 there is an idea about the same thing as Mass content adding is: Wiki data. Also, OmegaWiki is a complementar project to this two (i.e. "an implementation of Wikidata idea").
The idea is to continue with Mass content adding project (as one of the implementations of Wikidata), but using OmegaWiki as the database for translations. But, OmegaWiki is in alpha (or beta, I am not sure :) ) stage and there are a lot of issues which OW doesn't cover. One of the problems is that WZ doesn't cover gramatical cases.
Another big problem with WZ is that it is double lisensed (GFDL and CC-BY) which makes work on Meta incopatable with WZ. But, there are a lot of arguments pro for relaxing copyright for WZ data (and Mass content adding data). In general, data should be PD, but, AFAIK, it is not possible (so CC-BY is good enough).
A few moments ago, I found that it is possible that ordinary users edit OW outside of "Expression:" namespace. This solves a lot of problems.