please contact us (and the OSM Belgium board) via email at community at osm dot be
I’m sure one of the board members can answer your questions.

I’m not sure what you mean exactly with reconcile different languages on the map.
At this moment we tag the streets that have a Dutch and French name as
name : name fr - name nl
and also add name:nl and name:fr
We do the same for towns and villages.

We only do this for towns that are officially bi-lingual

AFAIK this is the same in Switzerland although they might use " / " between the 2 names instead of " - ".

I hope this gives you already an idea of the data. Since there is a name:nl and name:fr the render software can be configured to use that instead of the name field. that is how the Dutch and French version of the Belgian tile set is created.