Answering question 1:
There is no drop-down menu to select the directions language. You can select the language in the Directions geoprocessing tool, or you can set the directions language for a Vehicle Routing Problem layer using the following code in the python window:
proj = arcpy.mp.ArcGISProject("current")
mapObj = proj.listMaps()[0]
vrpLayerObj = mapObj.listLayers("Vehicle Routing Problem")[0]
solverProps = arcpy.na.GetSolverProperties(vrpLayerObj)
solverProps.streetDirectionsProperties.language = "pt-PT"
You do not need to install a language pack to get directions in Portuguese. All directions languages are available all the time, even without language packs. (This is new - ArcMap and older versions of ArcGIS Pro required a language pack installation to get directions in non-English languages.)
Answering question 2
We did not change the Solve Vehicle Routing Problem tool between ArcGIS Pro 2.5 and 2.6. Can you further explain your question?
Answering question 3
I am going to ask a colleague to help you with this question.