I have followed the tutorial on how to tranlate sugar to another language. This is almost done. I took all the en_us files from a default installation copied them renamed them and translated them. I have also translated and set the first day of week for the jscalendar.

However I have problems doing certain things in the backend now. Most of this is also done translating.

As soon as I install the new package even without changing the current language the module builder start playing up.
You can create a package, but when you try to add modules it states Loading..., Done and nothing is happening.

I have tried taking out the jscalendar files, no difference.
I have tried replacing different stuff in different modules with the original unchanged files, but I have not hit gold yet.
There are odd AJAX, json related issues reported in from different testers when they have the ang pack installed but not when they do not have it installed.

Removing the language pack and the problems disappear.

Have anyone else experienced this?

I have not yet downloaded another lang pack and tried with that.

Regards and thanks in advance
Ken