"a speaker" and "speaker" are the same thing. But Indonesian has a couple different ways to say "a" depending on the sentence. In terms of this sentence "I was asked to be speaker" would make no sense, hence the "a". You can not remove the "menjadi" or the sentence would be "I was a speaker".
Hello, I'm Indonesian. The phrase above "I was asked to be a speaker" is translated in Indonesian to:
I : saya
Was : - (we don't have past or future in our tenses, but sometimes if we need to say something past we say it: "telah")
Ask + ed : di + minta
To + be : untuk menjadi
A : seorang (to a person) sebuah (to a thing)
Speak + er : Pem + bicara
So the translation is:
Saya diminta menjadi pembicara,
Saya telah diminta menjadi pembicara,
Saya telah diminta menjadi seorang pembicara,
Saya diminta menjadi seorang pembicara,
Saya diminta untuk menjadi seorang pembicara.
All is right, I think all Indonesian will understand it.
I hope this will help.
in Indonesian there are no definite or indefinite articles. So you don't say "I want the apple" or "I want an apple", just "I want apple".
If you are talking about something specific and need to indicate it, you can add the suffix -nya (like "he took the book" --> "dia mengambil bukunya")
Indonesian also uses classifiers/counters. So when talking about specific quantities of things, you use these. Sometimes these translate to "a". Some examples of this are
I want three apples --> saya ingin tiga buah apel
he needs one stick of celery / he needs a stick of celery --> dia perlu sebatang seledri
Do you want an egg --> kamu ingin sebutir telur
Hopefully this clarifies a bit. Any questions please ask.