You could do something like this:
func _ready():
var big_text = "Lorem ipsum dolor sit amet"
var arr_str : Array = text_split(big_text, 2)
while arr_str.size():
print(arr_str.pop_front())
func text_split(text : String, size : int):
var text_array : Array
while text.length() > size:
text_array.append(text.substr(0, size - 1))
text = text.substr(size)
if text.length():
text_array.append(text.substr(0))
text = ""
return text_array