I had the same problem but just solved it. The pot file that comes with toolbox has some headers missing. But Poedit offered to fix them and this did the trick.
Here are the steps I took:
- Take the toolbox.pot file that is in the Toolbox theme language folder
- Change the file extension from .pot to .po
- Open the file with poedit
- On opening the file poedit says "Required header plural forms is missing". It also offers to fix it (click the button to the right of the error message) (Note I'm using version 1.5.4 of poedit)
- You get a screen called "catalog properties" with 3 tabs. You want the "translation properties" tab and on there the bottom field called "plural forms" (this is the bit that's missing and causing the error).
- For Dutch you need to put in the following in this field:
nplurals=2; plural=(n != 1)
- For other languages you can find what to enter here: http://translate.sourceforge.net/wiki/l10n/pluralforms
- Press OK to save your changes and that fixes the problem; you can now do your translation.
When you're done translating click "save" to have poedit save your new .po file and create a .mo file
Then change the names of these .po and .mo files to the naming convention for language files. For Dutch the files need to be renamed to "nl_NL.mo" and "nl_NL.po". For other languages you can find the language codes here: http://www.gnu.org/software/gettext/manual/html_chapter/gettext_16.html#Language-Codes
and the country codes here:
Now upload these 2 files into the Toolbox theme language folder.
Finally, check that wp-config.php has a language entry in it. If not create it by adding this line somewhere:
define ('WPLANG', 'nl_NL');
Hope that helps :)