ADDITIONAL SYSTEM INFORMATION :
OS: all the Linux distros
Java runtime: apparently from Java 8 the problem has been there

Here is the git page of fcitx: https://github.com/fcitx/fcitx5

A DESCRIPTION OF THE PROBLEM :
Many non-English speaker developers in Asia use Fcitx as their default IME under Linux. The problem is Java Swing application under Linux DE can't give or Fcitx can't read the correct position of a Java Window, so when we type CJK (Chinese, Japanese, Korean, etc.) using Fcitx, the IME does not follow the cursor and always appears at the left-bottom corner of the Java window, which is quite annoying. This bug has a long history, at least in some forums it has been there for more than 8 years. According to the developer of Fcitx, the Java application just does not tell IME the position information so there is nothing he can do about this. But I notice that under Windows, this is no such problem with Microsoft default IME. So, could the OpenJDK developers do something about this? Making Java under Linux actually provide position information for other IME? Thanks!