From what I understand, 'in' is translated as《på》when used in the context of being inside a building or room. Also, when saying "What's that in Danish?," you'd say, "Hvad er det på dansk." And anyone feel free to correct me as I am not a native speaker
Not quite. You are in the kitchen or bedroom... (i køkkenet/ soveværelset...) but "på badeværelset" on the bathroom. The bathroom is the exeption! If you are describing the action of going to the bathroom (as a physical location): "jeg går på badeværelset" or "jeg går ud på badeværelset" but going into another room, it would be "ind i". If shouting from the bathroom, it could be either "jeg er herude" or "jeg er herinde" - but the "correct" option is a matter of personal opinion. Leaving the bathroom, it is "ud af badeværelset".
Other uses of "på" (such as "hvad hedder der på dansk") are not really comparable to the use of prepositions in the pure physical sense.