While learning some katakana words, I noticed strange pattern with some of the loanwords, that originally end with “-en” or “-on” sound - in Japanese version that ending turns into “-un”.
I’m talking about a words such as
season - シーズン
lesson - レッスン
seven - セブン
open - オープン
Why don’t they keep the original vowel? Is there some kind of rule at work?
Now that you mentioned it, yeah, it seems right. (English isn’t my first language) They aren’t full-fledged “O” or “E” vowels when pronounced, so it makes sense to render them with Japanese ウthat can also be “muted” (like at the end of です).
Katakana-isation is far from a precise science. Just because you know how it’s pronounced in the original language, doesn’t necessarily mean you know how to write it in katakana.
One example is the city of Würzburg in Germany, which is spelled 「ヴュルツブルク」 (which is fine because we also have ハンブルク, ブランデンブルク, ルクセンブルク, etc). But the Würzburg radar (which was a military equipment in WW2) is 「ウルツブルグ」.