Translation overwritten after update

Hi,

We did make some translation of the .pot file with PoEdit. This create 2 files the .mo and .po files. After an update the files are disappeared. Where do we have to save this files, so there’re removed by an update?

First we put it in the plugins wp-content/plugins/xt-woo… folder, but here the files are removed.

We also tried to put the files in the wp-content/languages/xt-woo… folder but that doesn’t work (text is not translated). So were do we have to put this files to work AND not overwritten?