Translation of erstmals

You can always write me and we can learn together any language you want. How long you have taken classes? Was it only at night or on weekends? Makes me wonder how someone can be so fluent in Spanish.
I've been working on and off on the dictionary during the entire week, and I'll spend some more hours on it this coming weekend. Sometimes he would get a bit mixed up and use formal Castilian sometimes instead of informal.
These may be linguistic and cultural differences. There are indeed various regions throughout Spain and the word choice is not always the same. It is sometimes hard to understand people from other cities.