English strings in 4.0.1 nl_NL (and possibly other languages too)

In the nl_NL Support forumSupport Forum WordPress Support Forums is a place to go for help and conversations around using WordPress. Also the place to go to report issues that are caused by errors with the WordPress code and implementations. some users reported that there were some English stringsString A string is a translatable part of the software. A translation consists of a multitude of localized strings. in the nl_NL version. So I tested this and confirmed that the Add Media an Featured imange strings (and maybe others) were not translated. I discussed with my Dutch translations colleagues and Remkus said that he would build a new package for 4.0.1. After whcih I reinstalled, but the strings were still in English.

Then I saw a tweet of @pixolin where he stated that the same problem occurs/occured in the de_DE version of 4.0.1. His tip was to Update Translations in the Update screen. But, this was not available. Even after removing the po/mo filesMO files MO, or Machine Object is a binary data file that contains object data referenced by a program. It is typically used to translate program code, and may be loaded or imported into the GNU gettext program. This is the format used in a WordPress install. These files are normally located inside .../wp-content/languages/ in the /wp-content/languages directory.

Here’s what I did to solve this:

• Set language to English in Settings -> General
• Remove po/mo files in the /wp-content/languages directory
• Add define( ‘WPLANG ‘ , ‘nl_NL’ ); in wp-config.php (otherwise this cannot be selected in Settings -> General
• Set language to Dutch (Nederlands) in Settings -> General
• Remove WPLANG from wp-config.php
• Go to Dashboard -> Updates and click “Update Translation”

So, what went wrong here, and how can we avoid this from happening next time?