"My grandpa is teaching me to speak German."
Translation:Mi abuelo me enseña a hablar alemán.
Okay, trying to figure out when to include the “a”. Is it that it always follows conjugations of ensenar, aprender, empezar, and ayudar? Nope... just found this sentence... "Él quiere aprender italiano."
I had the same question so after some internet research, I found there's a list of verbs that require the proposition "a" between the conjugated verb and the infinitive that follows.
An obvious one that most people already know is "ir + a + infinitive" ("voy a comer" - "I am going to eat") but there are others. Enseñar is one of them. If enseñar is NOT followed by an infinitive, then you don't need the "a", such as "Mi abuelo me enseña alemán" (My grandfather teaches me German". But this DL question was "My grandfather is teaching me to speak German."
In this case, the "a" changes the meaning of enseñar from just "to teach" to "to teach how". This DL question is, in effect, "My grandfather is teaching me [how] to speak German." The other verbs on the list linked to above all have a slight shift in meaning with the addition of the "a".