The instrument names can be selected in German (or enter yourself). A transposed instrument gets the addition but then in English. As “Klarinette in Bb” 
and not “Klarinette in B”, which would be correct. Can you configure that somewhere? Or just omit the addition of transposition?
It seems that Dorico is internally wired to write notenames as “base + alteration”. This results in instrument names like “Klarinette (H Be)”, “Altsaxophon (E Be)” as you can see when you add new instruments.
I suspect that since German note names in general don’t use the alteration names (“Be”/“Kreuz”) but a different suffix (“es”/“is”), and because they don’t follow that simple scheme rigorously (G→Gis, A→Ais, C→Ces, F→Fes, but H→B, E→Es, A→As), this hasn’t been implemented yet.
At least, Bb is much better than H Be 
Thanks for the answer. I am often very unhappy with the operating concept of Dorico. It is very nice, if many things happen automatically. But only automatic? If there is “Klarinette in Bb” that’s a mish-mash, terrible. Denglisch! And I also find no setting that the transposition is not inserted automatically. For me Dorico is a nice fun, which saves me no time.
You can turn off all transpositions in staff labels by following the instructions here: https://steinberg.help/dorico_pro/v3/en/dorico/topics/notation_reference/notation_reference_staff_labels_instrument_transpositions_hiding_showing_t.html?hl=instrument%2Ctranspositions%2Cstaff%2Clabels
You can turn off transpositions on individual instruments via the Edit Names dialog, as explained here: https://steinberg.help/dorico_pro/v3/en/dorico/topics/setup_mode/setup_mode_players_edit_instrument_names_dialog_r.html?hl=instrument%2Ctranspositions%2Cstaff%2Clabels
We know that the handling of transpositions in languages other than English is not good enough, and it remains on our list of things to fix.