I’m Taiwanese, here is my view maybe not correct.
In Portuguese, Ihan = Beautiful(美麗), Formosa = Island(島)
The pronunciation of Formosa is 福爾摩沙.
寶島 means this island(島) has a lot of treasure(寶), because the variety of fruit, plants, animals, insects…etc. If Taiwanese say 寶島, sometimes has also praises Taiwan is a good place, and we use 寶島 more usually than 福爾摩沙.
It’s not common to say Formosa in Taiwan for Taiwanese , because it’s not instinctive to us, we usually say Formosa for introducing to foreign friends. Another small reason we not use Formosa in common is it’s not easy to pronounce and too long, haha.
Latin insula → Old Catalan illa → Old Portuguese illa → Portuguese ilha
English isle
French ile
Formosa is from Latin formosus, which is the adjective form of the Latin word forma, which is the English word form. It means the finely formed, i.e. beautiful.
Ilha Formosa of course means Beautiful Island, so the proper translation should be 美麗島.
寶島 is widely used in the Hanji sphere for treasure island. Famous menga artist Osamu Tezuka published a Shin Takarajima (新寶島, New Treasure Island) series in 1947, based on Robert Louis Stevenson’s Treasure Island.
So maybe the Japanese have also used the term to refer to Taiwan as a term of endearment, and the Late Immigrants simply continued the usage. I can’t exactly pinpoint when the term was first used to address Taiwan specifically.
So maybe the Japanese wouldn’t call Taiwan 寶島 as there already is one. Then again, if the Japanese could name one island 寶島, there’s no stopping them for nicknaming others 寶島…
Though one could argue that there are a bunch of places the Japanese named in Taiwan with similar/same names as in Japan, just like the KMT put all those place/street names we have from China. So 寶島could be one.
I want to write an article about how the KMT was making up Japanese styled Kanji names after taking over Taiwan for place names only with phonetic transliterations, when I have time.
Never heard of 美島, but 美麗島 is frequently used, especially by those in favor of Taiwan Independence. There’s a pro-independence magazine balled 美麗島 back in the 1970s which organized a mass demonstration in Kaohsiung on International Human Rights Day, 1979.
The KMT threw SWAT squads at the crowd, and tear-gassed the crowd. The police then followed up with a mass arrest island wide for those involved. 152 people were arrested, some of them were about to be issued death sentences, many of them tortured. Ex-vice president Annette Lu is amongst the tortured. It’s commonly referred to as the Formosa Magazine Incident (美麗島事件).
A team of liberal lawyers, including ex-president CSB and ex-presidential candidate Frank Hsieh, defended the protest organizers in a very hostile environment. All 8 accused were handed a guilty verdict, some of them fled out of the country. 5 of the 8 accused later became DPP chairmen.
A Kaohsiung MRT station is named after the incident, the Formosa Boulevard Station (美麗島站).
Many pro-independence songs also refer to Taiwan as 美麗島. The one titled 美麗島 is often suggested to be used as Taiwan’s anthem.
The song was written in 1977, but released in 1979, the same year as the Formosa Magazine Incident. So it’s no surprise that the KMT censored the song immediately.