Has the Arabic language changed from the time of the Companions to our current era, leading to a lack of understanding of some words in the Holy Quran, such as "عَدْل" (ʿadl) meaning ransom and "رِيش" (rīsh) meaning money or ornamental clothing? And does this explain the difference in their meanings from what is expected today?

What has changed is people's understanding of and knowledge of the Arabic language, not the language itself. A single word can have multiple meanings in the Arabic language. The examples mentioned — such as "al-rish" (feathers/wealth) and "al-adl" (justice/equivalence) — have multiple, expanded meanings in lexicon books, and they have not changed from their original Arabic وضع (state or condition); rather, people's knowledge of them has changed.