As of version 126.96.36.199, the Dutch language disappeared. This was due to the fact of the translations being below the 90% requirement. When a translation is less than the required 90%, it will not be included in the core. The Dutch translation was only one of them. German, Japanese and Russian was missing too, but these got added fairly quickly in the next release (188.8.131.52).
Having a lot of clients on concrete5 by now, I don't want the language to just go missing all of a sudden. So with the translations being at 100% now (for version 7), it will be included in the next update (probably called version 184.108.40.206). Hell yeah!
Version 8 of concrete5 is coming up as well and it comes with a lot of new translations too. I had the time to do a lot for this version as well, but it got stuck at 98%. As this version is not yet in beta testing, we still have some time to get it done. It will for sure be included in the core, as it's above the required percentage.
Do you have got it in you to translate as well? Get in touch, because the more translators we have, the better translations will be up-to-date and maybe even more languages get added to this already awesome CMS. Amen.