The [font=courier new]SweetHome3D.l4j.ini[/font] file is only for windows and you forgot to add an hyphen if in front of [font=courier new]-D[/font] Java option.
Under Linux, you should edit the [font=courier new]SweetHome3D[/font] file and add all the options cited in the FAQ Texts in the furniture catalog are not displayed correctly or icons in the toolbar appear very small on my computer. How can I fix that?. If you add only the [font=courier new]-Dcom.eteks.sweethome3d.resolutionScale=2[/font] option, it won't work because it's possible to change font size only in Metal look and feel.

There's no need to install Java since the installer provided in Download page already comes with a copy of Java 8. Anyway, I'm not sure that Sweet Home 3D is able to work under Java 9.