Yes, most words were inspired form existing English words. The caesar transformation words were mostly transformed from English words, some using Indonesian, some Arabic, some Latin.
I tried not to create a whole new word, instead the idea of adopting some words from existing language were a common practice on any language that we have now, so I tried to adopt whenever possible and change the pronounciation.
Here's an example of some words that was not adopted from an existing language (or if there was similarities, it wasn't my intention): - Vragel (soul) - Serentia (eternal) - Rus, Erus, Berus (the suffix used to implicate negativity, rus is least negative, erus is mid, berus is the most negative; e.g Vragelberus (to indicate a highly damaged, wicked, dangerous, or corrupted soul).
There's also some rule I used to create/adapt words, words that indicates greatness or something big always ends with the letter "A". E.g. Versila (universe), Elia (god), Alua (sky), Titania (giants), Manara (tower).
Name of places in the book also follows this rule. E.g Riddorana (place of huge waterfall), Zodiarchia (capital city), Altand (small ponds, note it doesn't end with an "A").
This rule allowed me to write poets that easily ended with the letter "A".
It is always interesting to learn words from existing language, then adopt it and learn how to make it fit with the existing language design.