Hm. There might be regional differences ...

In some regions, e.g. parts of the Allgäu, the Alphorn is traditional, while in other regions the Alphorn was not used at all ...

The answer to the question might also depend on the definition of "traditional", esp. how long an instrument must be used to be called traditional ...
Can the Akkordeon be called traditional? It was invented around 1825 IIRC.

I'd call the following instruments traditional (the list will be incomplete, these are the instruments that I remember right now) - English names given where I know them:

Zither
Hackbrett
Blockflöte (recorder)
Akkordeon
Gitarre (guitar)
Geige (fiddle)