人日本語学ぼうはミス頻繁で悔しい何ですか？

I understand what you meant to say, so I'd like to correct the sentence above.

Japanese has a completely different word order.

I would literally translate "日本語学習者がしがちな、相手を煩わせてしまう間違いは何ですか？" into Japanese.

Regarding conversational Japanese, I feel like it is hard for English speakers to pronounce long vowels and double consonants.

Sometimes such a mistake doesn't make sense to Japanese natives.

At the same time, for Japanese people, it is extremely challenging to make any sound in English.

I really think it is a pain in the neck for Japanese people to work on the accent reduction.

If you are a beginner or intermediate level, you could make grammatical mistakes in Japanese at the moment. 

However, you may need to focus on how to use Japanese particles as well as other grammar rules.

It would help you understand how to make sentences or speak in Japanese.

Keep up the good work.