What is it called when words like "what" and "how", aren't acting interrogatively, and aren't relative-pronouns?

Question

What's going on when words like "what" and "how" are used in the following, non-interrogative and relative-pronoun, way?

"Oh, [how] kind of you! My, [what] a nice young man you've become, love!"

Now, unless I'm an idiot (which is possible,) may I ask what these words are? And what they're doing? As I don't quite understand, and have recently began noticing them popping up more and more in my writing.

I also know these can't be relative-pronouns, as in Japanese, relative-clauses are made by putting the clause behind the noun-phrase being talked about:

"The student went home today." -> "To be the student who went home today."

「学生が今日帰った。」 -> 「今日帰った学生だ。」

This meaning of course that Japanese doesn't have relative-pronouns. However, Japanese still has these non-interrogative "what" and "how" words, one example being the adverb 何と (nanto).

So ya, what exactly are these words? What exactly do they do to speech? And why do they all seem to be, or be made from, originally interrogative words (何 means "what?")?

I've been looking and haven't found much, thus I ask.

Answer 1

What a good question! [sorry, couldn't resist that].

Now seriously, as you said you don't know, neither did I.

So I got to do a quick search on my favorite site [wiktionary] for this kind of questions, it gives you easy technical information to basically every word in the english language or any other language that's available there. It's really useful.

What I learned from it is that:
Those words are said to be adverbs.
And these adverbs function as intensifiers.

Then, when you use those words you are intensifying the meaning of other words, mainly adjectives, ya know That's it. How wonderful.

Answer 2

These are exclamative wh-words. Despite their resemblance to interrogative words, they are different, and the clauses they appear in have different syntax. Importantly, exclamative what is an adverb, whereas interrogative what is a determinative or a pronoun. The only two exclamative wh-words in English are how and what. The following examples look similar.

1. I understood what problems they had. (I understood what the problems were)
2. I understood what problems they had. (I understood the extent of the problems)

We can differentiate them, however, by making the relevant noun phrases singular:

3. I understood what problem they had.
4. I understood what a problem they had.

The evidence here shows interrogative and exclamative what to be semantically and syntactically different items. Because exclamative what is a degree adverb, a bit like such, it modifies the whole noun phrase and must occur before any Determiners as shown in (4). In contrast, the type of interrogative what seen in (3) actually is a Determiner, and appears directly before the noun.

So although these words look like interrogtive wh-words, they aren't!