English and French speakers are exceptional
I speak English and Thai fluently. Over the years I have at times had a spattering of Japanese, French and German, but no longer have any need for them, so have not bothered going any further with them.
Many, if not most people around the world are at least bi-lingual, with the exception of English speakers and the French.
I'd have to say many Thai people are quite xenophobic and stubborn about learning languages too, but with Thai being spoken by only a few tens of million in one country, they have little choice. That being said, there are a significant number of people in Thailand for whom Thai is a second language. That includes the Yawi speaking Muslim people of the south and the various hill tribe people of the North. In the Northeast millions speak Lao, which is similar enough to Thai to be considered a dialect. It is those marginalised, already bilingual people who seem more successful at learning new languages.
I learned Thai initially at a six week immersion course. At the end I could make the sounds, read and write the alphabet (which is highly phonetic, but when written does not have a space between the words), and understood a few words. From there its was just a matter of using the language and picking it up as I went, just like a kid picking up his or her own native language. Where I lived at the time there were very few English speakers, so I had little choice.
It took about six months to become reasonably comfortable with Thai. After that it developed quite quickly. That is in keeping with the experience of others.
I didn't translate. At first I would use either English or Thai, but not both at the same time. It was several years before I became confident enough to interpret simultaneously.
I no longer write, and read only a little; I have no real need to do either, but could probably become literate quite quickly if necessary. However I do think that learning to read and write a language helps in the formative stages of learning.