"There are many balls."
This is not a matter of outdated spelling practices, but of shallow versus deep orthography. Korean uses deep orthography where underlying phonemic details are documented in spelling.
The pronunciation depends on context:
A spelling can be pronounced differently depending on context, thereby providing some regularity to spelling at the expense of extra mental resources to compute the sound from the spelling. It’s an idea called morphophonemic spelling, which many languages have but others do not. Turkish is a language that does not feature morphophonemic spelling since it spells words exactly as they are pronounced and not as they are mentally represented—as phonemes.
Korean, as it exists today, had its spelling modernized several times in the past century with efforts spearheaded by joint Korean and Japanese institutions which largely shaped the language as it exists today. The last time it was touched was just 60 years ago. Prior to the twentieth century, Korean Hangul spelling was erratic and left up to the whims of the particular writer. Words were spelled as French is today—with superfluous etymological spelling (which were not always correct in Korean anyhow). 많다 is a relatively new spelling specifically devised to reflect the fact that the ㄷ becomes a ㅌ after the verb root, and any other consonant that gets near will become aspirate as well. Before the advent of morphophonemic spelling, this was spelled in various ways—most commonly as 만타—with other conjugations using 만-, which made learning and teaching such verbs difficult as the roots were not contained in something definite. Today, we have the sanity of an invariable 많 tacked onto an invariable 다. So, the spelling was never intended to prescribe a pronunciation of [nh] as TheRealRial suggests, but to reflect the fact that the root has an inherent ability to aspirate a following consonant should it get within striking distance!
Yup. They added back letters that were not there before. For example, we have modern French 〈doigt〉 meaning “finger.” But the old French spelling was 〈doit〉/〈doi〉. Some scholars had decided to add back letters from the Latin source of the word: 〈digitus〉. Thus, they have the spelling 〈doigt〉 in which the 〈g〉 is not pronounced in any of the inflections. In English, we have the word 〈island〉, one of the delightful examples of English scholars sticking letters that don’t even belong there etymologically. I’ll let you read up on the history.
- Korean doesn't allow for more than two consonants to be pronounced in succession, so when there are two consonants at the end of a syllable, they are only both pronounced if they are immediately followed by a vowel. 2. nh isn't the smoothest pair of consonants to articulate, so you'll often hear people don't pronounce the h at all. 3. Some spellings in any language are out of date and don't quite resemble contemporary pronunciation (something English is rather infamous for)