I don't think you can. From the FileChooser
Javadocs:
Provides support for standard platform file dialogs. These dialogs
have look and feel of the platform UI components which is independent
of JavaFX.
Since these are native File Chooser dialogs, the text displayed in them will be controlled by the locale of the platform (i.e. the regional settings chosen on the user's machine at the OS level). Note that this is probably what you want anyway, as the user likely has these set the way they want. You could experiment with changing your regional settings and seeing if it changes the file chooser.
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