How do you say 'I want to learn Japanese'
And how to pronunce it if possible please thanks.

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Answer

I would say it this way, I think it's correct...

日本語を習いたいです (Nihongo wo naraitai desu)

I'm not sure how to explain pronunciation but I'll try

A sounds like the one in father
E sounds like the one in death
I sounds like the one in is
Both O and WO sounds like the O in pot
The U in desu is silent you pronounce it dess
The no silent U sounds like a double O like in book

I hope that helps you

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Hi. 
I am Japanese.
What Mine wrote is totally correct :D

Answer

Watashiwa nihonggo kotoba wo benkiyo shitai desu.

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I want to learn japanese can be said as 
" Nihongo wo narabitai desu ".
Narabemasu - learn.
Masu form + tai means want to do something
Masu form of Narabemasu is Narabi
i hope its useful for you