In Custom Translator service, when I create project it only shows pairs that is some_language -> English or English -> some_language. How can it help when I want to translate between two languages which do not include English? (i.e. Chinese -> Japanese)
In addition, can I use custom translator when I trying to translate more than one target languages?
You need to train two models, pivoting through English, in the same workspace. Then you can make an http request to your category, setting the from as Chinese, and the to as Japanese.
You can do the same for several other target languages (e.g. Korean, German) and then specify a list of to languages in the http request. docs link