Make time tracking input respect i18n shortcuts for weeks, days, minutes, etc.

Not entirely sure of this is the best idea however it can be helpful to users:

When I enter a time span for the "Filterabonnement" in days (according to the "Examples," the abbreviation for this would be "t"), I always receive an error message saying that I must enter a valid time period. The problem is that it only works with "d" (for the English "days").