I have the same issue here.
I just installed Membership Pro.
Then I installed the language pack with the Dutch translation.
When I go back to the backend => Components => Membership Pro, then th backend texts are all in English.
Normally Joomla will recognize that the default language is Dutch and it wil check if there is ann nl-NL-xxx.ini file for frontend and backend. If these files are installed, then the backend will be changed to Dutch.
The files are there. I checked it by using FTPsoftware.
But the backend is still English.
I don't think I have to translate extra fields, cause what I wrote above is not happening.
So what can I do to have a Dutch Membership Pro backend?
The language file for the backend was broken.
It is fixed now and the new language file is added to de Downloads here.
So if anybody else have problems with the Dutch language, please download the latest translation and install it over your existing files.
And for everybody who will trabslate languiage files in the f=uture, please don't use " in the middle of your translation.
In that case use the single '.
A " in a translation will break the file.
Thanks to the OSSolutionteam who fixed it this time.
Thanks Wouter. Just want to add that if you translate the language file from Membership Pro -> Translation, you can still use double quote character. The system will handle it automatically on save (add \ character before that one) and it will work well