日本語（にほんご）先生（せんせい）をなります is NOT a correct sentence. So how would you fix it?
If I ask my Year 12 students, they will straight away say:
Yes, that’s quite a bit better. なります means “to become.” As “a Japanese teacher” is not an object of the verb “become” (but something that you turned into), you cannot use the object marker を with it. Instead, you should use に.
But with my response “quite a bit better” will probably prompt my Year 12s to say:
Yes, that is a lot better. You do need the noun joiner の between 日本語 and 先生. With Year 12s I think I can stop right here.
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