Imperturbable (adjective) — هادئ وثابت: Calm and not easily upset. Below are 8 words with a similar meaning; the linked ones have full GL Dictionary entries with their meaning in Arabic.
Peaceful; tranquil; serene; composed; quiet; still; undisturbed
Calm, self-possessed, and poised — composed names the still state, not compose (to write), not compose-yourself (calm down now), and not composed-of (made of…
Cold; calm; composed; excellent; fashionable; relaxed; moderate; stylish
unflappablesereneunruffledcollectedpoised
Calm and not easily excited.