The Greek that is translated as “one stroke of a letter” or similar in English is translated in the German New Testament translation by Berger / Nord (publ. 1999) with ein i-Punkt or “one dot on the i.”
In Matthew 5:18, the Greek that is translated as “not one letter, not one stroke of a letter” in English is translated as kein Punkt und kein Komma or “no period and no comma.”