I think this is a stupid question.... but... (read below)?

Question

as far as I understand Hebrew has no vowels. Is this indeed the case? If so, how do people that read Hebrew know what vowel to insert? Because spoken Hebrew does have vowels. Are there any other languages that have no written vowels?

Answer 1

there are vowels in the language but not in the alphabet of the Hebrew language. The same goes for the Arabic alphabet.

The writer and the reader sort of have an understanding which vowels should be where. And they use special other symbols to indicate that there should be a vowel. You can see them as little dots over and under the normal text.

Other language without written vowels to my knowledge is Chinese

Answer 2

It is not a stupid question at all!

The Hebrew writing system indeed does have no vowel letters (though four Hebrew letters can be used for writing vowels as well as consonants). Like in other Semitic languages (such as Arabic or Phoenician), the basic meaning of words in Hebrew is determined by roots (so-called "radicals") that consist of (mostly three) consonants. Different vowels between those consonants indicate either different regional variants (dialects) or words derived from the basic meaning:

Hebrew כתב (k-t-b) can be read as kátôb 'to write‘, kátab 'he wrote‘, kátûb, ketîb 'written‘, kotéb 'writing‘ etc.

Similarly, the same root in Arabic:ك ت ب (k-t-b) can result in:كتب (kataba) 'to write', كتاب (kitâb) 'book', كاتب (kâtib) 'writer, writing (active participle), مكتوب (maktûb) – 'letter, written text/document' (passive participle) , مكتب (maktab) 'writing desk', مكتبة (maktaba) – 'library, bookshop'

In order to distinguish meaning of words in Hebrew writing other than purely by their context, vocalisation systems were developed, using little diacritical signs underneath, over, or within the letters. In particular cases, the vocalisation is purposefully wrong, such as in the wrong vokalisation of the Hebrew name of god (Y-H-V-H) as "Jehovah", so that it was not inadvertently spoken out while reading holy texts (the first commandment forbids to speak out god's name).

Other languages that do not function in the same way as the Semitic languages, do need vowels in their writing system. Thus when the Greeks (speakers of an Indo-European language) took over the Phoenician alphabet (from which Semitic alphabeth the Hebrew alphabet is also derived), they had to adapt it by complementing it with vowel letters. The same goes for Latin and Cyrillic alphabets which are in turn based on the Greek Alphabet.

There are (largely) Indo-European languages written with the Hebrew alphabet, such as "Ladino" (Judeo-Spanish, Spanyol, Judezmo), the language of the Jews living in Spain before they were expelled by the "Reyes Catolicos" Ferdinand and Isabella in the 15th century and mostly found refuge in the then Ottoman regions of the Balkans; or Yiddish. Their Hebrew alphabets needed additional vowel letters.

Answer 3

They already explained it... better than what I could have done.
But you might think it is just too weird to try to remember which words are pronounced with what vowels.
But... you speak English. Of course it is no the sdame, but... how do you know the sound the letter "i" must have in "image" or in "mine"? Aren't they the same letter? You just know... you learned it by heart. And.. I think you will never have doubts about how to pronounce it in each of those words. A similar process occurs in those languages.