Italian speakers often have a confusion on the different uses of "any" and its different meanings.

Any is usually defined as being an adjective, an adverb, a pronoun, a determiner and until today I was unaware of a further subclass: a numeral

Many words of different parts of speech indicate number or quantity. Quantifiers do not enumerate, or designate a specific number, but give another, often less specific, indication of amount. Examples are words such as every, most, least, some, etc.

Hence, "any" has a similar meaning to "a" and is normally used with uncountable and plural nouns.

• I haven't got any books. (singular and plural noun)
• Do you need any information? (uncountable noun)

There are quite a number of different uses of "any" and its compounds e.g. anything, anyone etc.. but to begin with these will do:

Examples and explanations taken (and adapted) from Practical English Usage by Michael Swan:

"Any" meanings and uses:

1. It doesn't matter which

• It's my treat. Choose any dress you like.
• Take any card.
• Any book on grammar will tell you how to use "any".

2. In questions and negative sentences "any" can be used with comparatives, with "different" and in the expressions any/good, any/use, and any/point.

   • Is she any better?
   • I can't walk any further
   • You don't look any different now than ten years ago.
   • Is there any point in carrying on?
   • Was the film any good?

3. In sentences with negative adverbs such as never, hardly and rarely

   • He never has any spare time
   • She hardly eats anything
   • They rarely visit anyone

Italian speakers are often confused by the different uses of "any" and its different meanings.

Any is usually defined as being an adjective, an adverb, a pronoun, a determiner and until today I was unaware of a further subclass: a numeral

Many words of different parts of speech indicate number or quantity. Quantifiers do not enumerate, or designate a specific number, but give another, often less specific, indication of amount. Examples are words such as every, most, least, some, etc.

Hence, "any" has a similar meaning to "a" and is normally used with uncountable and plural nouns.

1. (a) Do you have any books? (plural noun)
   (b) I haven't got any books.
2. (a) Do you have a book? (singular noun)
   (b) I haven't got a book
3. (a) Do you need any information? (uncountable noun)
   (b) I haven't got any information.
4. (a) *Do you need a information? NO
   (b) *I haven't got a information. NO

Examples and explanations taken (and adapted) from Practical English Usage by Michael Swan:
"Any" meanings and uses

1. It doesn't matter which

• It's my treat. Choose any dress you like. [Choose a/one dress]
• Take any card. [Take a/one card]
• Any book on grammar will tell you how to use "any". [Any one book = every book on grammar]

2. In questions and negative sentences "any" can be used with comparatives, with "different" and in the expressions any/good, any/use, and any/point.

   • Is she any better?
   • I can't walk any further
   • You don't look any different now than ten years ago.
   • Is there any point in carrying on?
   • Was the film any good?

3. In sentences with negative adverbs such as never, hardly and rarely

   • He never has any spare time
   • She hardly eats anything
   • They rarely visit anyone

As a result the OP's phrases:

It can be found in any book
It can be said in any language
This can be understood by anyone (i.e. any person)

mean it doesn't matter which book/language/person, because every book/language/person has this quality or ability.