Learning PEI but also important things about languages: inflection, casing, etc: Start at https://youtu.be/kzP5Lq9fYi8?t=475
Difficulties in Systems design: A complex system that works is invariably found to have evolved from a simple system that worked. A complex system designed from scratch never works and cannot be patched up to make it work. You have to start over with a working simple system.
1. noun, 2. pronoun (in place of noun), 3. adjective (describe noun - attributive, predicative, comparativ), 4. verb, 5. adverb (modify verb), 6. preposition, 7. conjunction, 8. interjection
World Atlas of Language Structures (WALS) is a large database of structural (phonological, grammatical, lexical) properties of languages gathered from descriptive materials (such as reference grammars)