I don’t use Organic Maps a lot but indeed it has a strange default mode when adding points in multilingual territories, like Belgium.

When you fire the "Add a place to the map" it looks like it shows several text boxes with a language name.  There is a small hack here: hit the "Add a language" option and scroll down to the last one named "Native for each country" → add the name only there and you will be fine.

I reported the problem to the devs because we get overwhelmed by this problem since OM is becoming popular.

Happy mapping!