China

Article 34 states:

All citizens of the People's Republic of China who have reached the age of 18 have the right to vote and stand for election, regardless of nationality, race, sex, occupation, family background, religious belief, education, property status, or length of residence, except persons deprived of political rights according to law.

Excerpt from the Constitution of the People's Republic of China (1982, last amended 2004)

Article 24 states:

...Citizens who suffer from mental illness and are incapable of exercising their electoral rights shall, upon determination by the election committee, not be included in the roll of voters.

Article 36 states:

…If a voter is illiterate or handicapped and is therefore unable to write his ballot, he may entrust another person to write it for him.

Excerpts from the Electoral Law of the National People's Congress and Local People's Congresses of the People's Republic of China (1979, last amended 2004)