"She reads the dictionary and she speaks the language."
Translation:Léann sí an foclóir agus labhraíonn sí an teanga.
Are these letters referring to the initial consonants of the word not to be lenited? What do the final three DTS stand for?
Can the second "si" be missed in Irish as in English when you could say "she reads the dictionary and  speaks the language"?
No. In English, the subject comes before the verb, so the first "she" is still, technically, before the 2nd verb. In Irish, the subject comes after the verb, and if you left out the 2nd sí, the 2nd verb wouldn't have a subject.