At the moment there is only one variant of Spanish. https://en.wikipedia.org/wiki/Spanish_dialects_and_varieties doesn't seem to explain the difference very well or whether there is a standard orthography for this dialect. Can you clarify?
The main difference is the use of voseo rather than tuteo (you can read about both on Wikipedia if you are unfamiliar with these verb forms). We also don't really use the word tú ever. You can read more about Nicaraguan Spanish at wikipedia https://en.wikipedia.org/wiki/Nicaraguan_Spanish