has or have

Well, that's goofy. It's a singular nation with a plural name. The same is true of "The United States Of America", but nobody ever uses a plural for that. Another is "The Maldives", and there are some more, but always a singular verb.

Thanks, Jewels Vern.

I think you haven't answered my question whether it should be has or have?

It is one of the few Asian nations that has/have achieved a high ranking.

I would use ‘has’.

Has is correct, it refers to one.

It is one of the few Asian nations that has achieved a high ranking.

Contrast with
A few Asian nations have achieved a high ranking.

Thanks, izzythepush.

Doesn't "have" relate to "a few Asian nations"

It is one of the few Asian nations that have achieved a high ranking.

Does this help?

if you use a few different words and make the sentence read "Germany is one of the few European countries that has achieved a high ranking". I think it may be confusing seeing "one nations" not "one nation".

If Izzy is online, he will be able to improve on my example.....Izzy, are you online??

Izzy is correct.

It [...] has achieved a high ranking. Germany is the subject of the sentence.

I am now, but it's a bit late.

Have relates to few meaning more than one. That's why I amended the sentence slightly to make it work. By putting one of back in you've made it wrong.