At translatewiki.net we support many languages and many applications. As a consequence, it is important that the rules that apply for a language are consistent and correct. It is not just MediaWiki any more that is affected, it is also StatusNet or OpenStreetMap to name just two. The people administering translatewiki.net do not know what linguistic rules for a language are correct. It is equally plain that it is impossible to learn about and judge all the possible issues.
It is quite fortunate that Unicode in its Common Locale Data Repository (CLDR) provides a framework where the linguistic building blocks necessary to support a language are provided. That is, for as long as the information is correct and, for as long as people took the trouble to provide the information for their language.
The benefits of insisting on good information from the CLDR are huge; the CLDR provides the essential data for many other applications for instance, once this data is complete, a language can be supported in Open Office.
Unicode provides translatewiki.net with the surety and stability it needs.