Summons as the accused: prepare the interview and know your right to silence.
A summons as the accused is the most common reason for first contacting a lawyer. Under Section 49 StPO you have the right to remain silent, the right to a defence lawyer and the right to speak with that lawyer before questioning. No one has to incriminate themselves. From a legal perspective, what matters now is to obtain access to the file under Section 51 StPO before making a statement, or at least to clarify the exact allegation, because any statement made without knowing the allegation is a risk.
As a German accused you also have the right to an interpreter under Section 56 StPO if you cannot follow the language of the proceedings well enough. Do not ignore the summons itself, an unexcused failure to appear can lead to a forced appearance. The correct route is to coordinate the appointment through a defence lawyer.