Germany

Section 13 states:

A person shall be disqualified from voting if  …

• (2) a custodian has been appointed not only through a restraining order to attend to all his or her affairs...
• (3) he  or  she is accommodated in a psychiatric hospital  under  an  order  pursuant to Section 63 of the Penal Code in conjunction with Section 20 of the Penal Code.

Section 14 states:

• (5) Persons eligible to vote who are illiterate or prevented by a disability from casting their vote may avail themselves of another person's assistance for that purpose. Such support shall be limited to practical assistance in communicating an electoral decision that has been taken and expressed by the person eligible to vote. Such assistance is inadmissible in cases where an abusive influence is exercised while it is rendered, where it replaces or alters the self-determined opinion-forming or decision taken by the person eligible to vote, or where there is a conflict of interests for the person rendering assistance.

Excerpt from the Federal Elections Act (1993, last amended 2013)