Unlike missionary work in Africa and South America they were not able to have a big influence in society.
Christianity seems somehow to be incompatible with Buddhism, scoring the world's lowest Christianity percentage in S-E Asia across the world. In most countries like China and Japan they had very little success.
In fact in Japan, trading was finished with the Portuguese because they brought too many missionaries in the country, disturbing their highly developed culture, in favour of the Dutch who understood the problem and promised just to stick to trading and were granted the trading monopoly on the small island of Deshima and were prohibited from going into the rest of the country.
Exceptions to the rule are the Philippines where for long time the Spanish and later the American missionaries successfully succeeded to f*ck up things thereby ruining the original country's culture and Indonesia which was occupied by the Dutch for about 150 years.
Christianity is still growing in Thailand, but (fortunately) Thai population grows more fast than the new Christians, resulting in 0.8% or less than 500,000 souls at this moment.
Especially in the North and along the North-Eastern border, where the very poor people live, missionaries scored bigger successes, especially with Laotians living in Thailand and former Myanmar hill-tribe people like the Karen tribe. When visiting the long-necks near Chiang Mai at the end of the village I was disgusted to see a Christian church, apart from the fact that a part of the whole tribe was moved there as a human zoo in 2005, easily reachable by taxi from Chiang Mai.
Now Christian missionaries gave up the direct approach and are into doing good work building their own hospitals and training centres, thereby retrieving once in a while a new lost Thai soul.
Nearby my mansion there's a small Catholic institute which gives vocational training to (bar)ladies and ladyboys, like English language, computer lessons, hairdressing and massage, all free of charge.
They hold three masses on Sunday at different times: One in Thai at noon, later one in Italian and after that one in French.