You have to download the updated Language.xml file too otherwise it won't work.
This server also haves optional extras.
The English XML file is there to change the original descriptions to the Flash version descriptions, which are mostly more detailed and longer.
The WaveBank XWB file is to switch the Main and Jazz music to the Mobile and Flash versions.
This does not work on the BTD5 Windows 10 Store version, because the folder of it is too heavy protected by Windows.

Dutch Bloons TD 5

Here you can download Bloons TD 5 in the Dutch Language for the Steam version.  Also includes BTD 5 flash descriptions for Steam in English.

Voter pour Dutch Bloons TD 5