>>47747708No, Japanese uses transliterations. You use the closest equivalent sounds for foreign words.
ダイヤモンド = Daiyamondo = Diamond
ディアルガ = Diaruga = Dialga
Dialga specifically doesn't use a Daiya sound, it uses a Dee-a sound, it's a corruption. Similarly,
パール = Paaru = Pearl
パルキア = Parukia = Palkia
It's not パールキア (Pearlkia), but パルキア (Palkia). Up through the DS games, the character limit in the Japanese versions was 5 as well, which is why they use ダイヤ (Daiya; Dia) as a potential default name for the main character instead of the 6 character ダイヤモンド.