Q: Is it duplicate submission if a small part of two papers in two different languages is the same?

If only a small part of the content is the same in both papers, it is more likely to be considered a case of self-plagiarism rather than duplicate submission. However, either way, it is not really ethical unless you are transparent about it. Therefore, it's best to cross-cite the papers, that is, cite the Chinese paper in the English one and the English paper in the Chinese one. However, since you haven't submitted either of the papers yet, it might be a good idea to put it a comment or a footnote saying that the cited work is still not published and that you will update the citation once the paper is accepted for publication.  

Do go through the following posts for more information on plagiarism:

• PODCAST: 5 Common forms of plagiarism and how to avoid them
• VIDEO: 5 Easy tips to avoid accidental plagiarism

We also have an excellent course on How to avoid plagiarism that you might find helpful.