You’d use ”om” (about), preferrably with the verb ”handla (om)” (to deal (with); to be (about)”: Presentationen handlar om svenska. or you could also say Presentationen är om svenska.
It was "exercises in German" i believe. It was also discussed in the comments that "i tyska" implied that they were exercises in a German language class and "på tyska" meant the excercises were in the German language.
Perhaps lärare i tyska? (Teacher in German). In that case the language name is a subject and then you use it, but in Swedish you speak on languages, rather than in.
Is it correct to say "The presentation about France is in German." as "Presentationen om Frankrike är på tysk."?
Korrekt svenska är [correct swedish is]: "Presentationen om Frankrike är på tyska."