My first foray into eastern Asian constitutions will focus on Japan. Japan’s constitution was ratified in 1947, so it is a consciously post-war document.
The first mention of religion in the Japanese constitution is as follows (where I’ve interpreted “creed” to include religious identity):
All of the people are equal under the law and there shall be no discrimination in political, economic or social relations because of race, creed, sex, social status or family origin.
Then, we have two very clear statements concerning religious freedom and state-church separation:
Freedom of religion is guaranteed to all. No religious organization shall receive any privileges from the State, nor exercise any political authority. No person shall be compelled to take part in any religious act, celebration, rite or practice. The State and its organs shall refrain from religious education or any other religious activity.
No public money or other property shall be expended or appropriated for the use, benefit or maintenance of any religious institution or association, or for any charitable, educational or benevolent enterprises not under the control of public authority.
This last statement goes pretty far: no government support for any charities not actually run by the government. i.e., no tax breaks for charitable organizations (since this would constitute public money). It’s not clear that this is how things are working in Japan today – tax breaks are, to the best of my knowledge, permitted for donations to non-government organizations (see here). No amendments have been made to the constitution.
That’s it for religion in the Japanese constitution – short and concise, just the way I like it!