If you're thanking someone who is close to you but is also older than you, this form indicates a polite respect for the person's age. However, this is still considered a relatively informal phrase and should not be used with strangers. If you use 고마워요 (go-ma-weo-yo) with people you don't know, this polite phrase suddenly becomes rude. If you're not sure if it would be okay to use this phrase, use one of the formal expressions of gratitude instead. This phrase is very informal and is considered appropriate only if you're talking to close friends or family members around your age or younger than you. If you have a lot of Korean friends or are going to school in Korea, you may find that you use this quite often. Avoid using this phrase to say "thank you" to anyone you don't know, even if they're considerably younger than you, unless they are small children. Casual Korean is never used between adults who are strangers, even if there is a significant age gap between you. If you say 정말 고마워요 (jeong-mal go-ma-weo-yo) or 정말 고마워 (jeong-mal go-ma-weo), you mean something similar to "thank you very much" or "I'm very thankful." You can use this if someone really goes out of their way to help you or if you just want to sound sincere.  You can add 정말 (jeong-mal) to the beginning of formal expressions of gratitude as well. For example, if you lost your passport in a restaurant and a server helped you find it, you might say 정말 고마워요 (jeong-mal go-ma-weo-yo) to them. You can also add 정말 (jeong-mal) to be more emphatic about turning down something offered to you. For example, you might say 아니요 정말 괜찮아요 (a-ni-yo jeong-mal gwaen-chan-a-yo). In context, it's a bit like saying "No really, it's okay, thank you" or "Thank you very much, but no" in English.

How would you rephrase that briefly using Indonesian?
Gunakan frasa “고마워요” (dibaca “go-ma-weo-yo”, dengan vokal “eo” dilafalkan seperti gabungan bunyi “e” pada kata “kenapa” dan bunyi “o” pada kata “bola”) jika Anda tetap harus menggunakan gaya bahasa yang sopan. Katakan “고마워“ (dibaca “go-ma-weo”) saat berterima kasih kepada sahabat atau anggota keluarga. Tambahkan kata “정말“ (dibaca “jeong-mal”) sebelum frasa terima kasih untuk menandakan rasa terima kasih yang lebih dalam.