Encoding / supporting multiple languages

Hi, 
I'm working on a font that an agency want to use in a campaign and different agencies across Europe will be using it. It has to support some central European languages as well western European users. 

I'm currently using Fontlab and have the Default Encoding set. When I need to add in a glyph that doesn't have a spot already there, I switch to MacOS Central Europe, find it there and it add it before switching back to Default Encoding. 

Is the best way to do things? If I continue like this will the font work for someone in Turkey or Poland, for example, in the normal way they would expect?

Any advice would be much appreciated. 

Thanks
Pascal