The tunic is from the Scots Guards, a senior UK infantry regiment, because of the buttons grouped in threes and the thistle on the collar.
The distinctive hat is a "shako". They were used in British uniforms in the past, but this one bears the letters "VMI" standing for "Virginia Military Institute", a military college run by the state of Virginia in the USA. (Thanks https://history.stackexchange.com/users/22536/kimchi-lover for pointing this out in comments.) Therefore, just from these two elements, we can see that the overall uniform is a mashup.
For the remaining bits and pieces -
The gold-tasselled epaulettes (shoulder boards) are clearly added on top of the originals. Fringed epaulettes were historically used in foot guards' uniforms, but were replaced in the mid-19th century by the black tabs which can be seen here under the gold ones. Several countries use epaulettes like this and it is not obvious from the pictures where these ones come from.
The gold aiguillette (rope thingy that comes down from the right shoulder) is worn by certain British officers of high rank or with royal associations, such as aides-de-camp to the Sovereign. Again, other countries use the same braid but with a different meaning; Americans similarly reserve the gold aiguillette on the right shoulder for Army aides to the President.
I do not recognize the black and gold sash. Update: kimchi lover in comments below recognized it as the sash of a Russian decoration, the Order of St. George, First Class. This was awarded 1769-1917 and revived in 2000. It is meant to be worn with the cross-shaped medal hanging from the sash, and with an additional diamond-shaped star on the left breast, here apparently absent. As the original Order was given exclusively to 25 very notable individuals, this is likely not an original sash but a replica.
As pointed out in comments to the question, the large pointy blue medal is the Prussian "Pour le Mérite", later continued as a civil medal of Germany. The other medal could be a US Air Force Good Conduct Medal, judging mainly from the ribbon.
The belt is not original to the tunic (it would be white). With a better picture of the buckle it might be possible to say something further.
The sword is also hard to see. There is clearly some sort of design on the pommel (the blunt end) which might tell us more. From what we can see, it has a solid guard (the flat piece between the part you hold and the part that is sharp) rather than one made up of lots of fancy loops, which might help in narrowing it down. Update: R Leonard in comments suggests it is an officer's sword from the US Navy, which seems plausible, especially from the pommel.
In toto, we have elements here from at least the UK, USA, Imperial or contemporary Russia, and Prussia. I expect that these were not all worn by the same individual - he would have had a distinctly varied career. In terms of dating, the USAF medal was first awarded in 1963. It could plausibly have come from an Air Force member stationed in Taiwan prior to their withdrawal in 1979. On the other hand, the Prussian version of the medal was last awarded in 1918, though there is a modern version with different insignia (a ring rather than a cross). Probably, the shop owner has assembled this collection from a variety of sources, and not necessarily relating to any particular events in the history of Taiwan itself.
