How to say in Czech: How good is his Japanese?

English
How good is
Czech
Jak dobře umí japonsky?
His Japanese is getting better.
His Japanese is very good.
How do you say that in Japanese?
I do not speak Japanese very well.
You speak Japanese very well.
His native language is Japanese.
Is he learning Japanese on his own?
He is Japanese.
He is learning Japanese.
He is not Japanese.

Czech phrasebook and translator with tens of thousands of sentences translated by humans. Czechslator is being developed by Michal Měchura. CREDITS Czechslator's sentence generation engine is partially based on Grammatical Framework. All Czech pronunciation is computer-generated using Microsoft Azure Text to Speech. When Czechslator cannot find a translation in its own database, it looks in the PanLex dictionary or obtains a machine translation from Microsoft Translator. PRIVACY Czechslator does not save any cookies in your web browser and does not collect personally identifiable data. Czechslator uses StatCounter for traffic analysis, configured not to save any cookies in your web browser and not to collect any personally identifiable data.