Source from: http://ujop.cuni.cz.
You should set realistic goals. For example, it is unlikely for the average learning to go from A1 to C1 in 28 days. Although if you are a complete beginner aiming for A2/B1 is pretty realistic with a good plan in place.
It is really important to set a budget for language learning and have resources in place before you begin. If you are kickstarting a 28-day language learning challenge then it may be a good idea to take advantage of the FREE 1 month trials a lot of language learning companies have to offer. This will be enough time to grasp all the basics required.
If you have any questions about the planner, please contact me