Add translation files to custom module doesn't work I've created translations files with poedit called nl_NL.mo and nl_NL.po and added them to a 'translations' folder within my custom module.

Now when I try to re-install my module; the translation isn't being imported.

Could this be because my default language is NL or is some other issue?
You might need to uninstall the module completely and reinstall it again, in order to be able to import the translations. Otherwise, they are not picked up automatically. There are a couple of threads in the Drupal forums mentioning this issue: https://www.drupal.org/node/220341 , https://www.drupal.org/node/435706#comment-2711736 

Hope that helps,