Old Czech (Bohemian) or Moravian

[pjburkshire]

However, what could be the reason for using a single symbol for L and R? How distinguishable are they? What was the motivation of the alphabet’s creator (did they want to make things more convenient, did they consider these two sounds to be the same, or something else)?

The reason would be that writing in the Czech language (and not Latin or German or Old Church Slavonic) was something new and still under development.  I'm assuming that the creators of the Voynich Manuscript were not linguistics experts and were going with what sounded right to them at the time.