There are two number for the frame size.
The current default is 729,578. You can change both at the same time and it should work fine.
May be you need to change value in english tab.
The default language is english when double click jar file to run it. I am asking the author of EJS to find out is it possible to change default language in java application mode.

But if the jar file was loaded into html page (shown as applet), the browser will select the locale and change it to the default language.
You can view this [u]web page source[/u] if you want to know the [u]tag for the applet[/u].

I certainly hope you can upload your translated jar file as attached file (Click "[b]Additional Options[/b]" to find upload options). If you use the "[u]upload new EJS jar file[/u]", then the jar will be turn into html code to shown applet at the end of the posted message. Because we already have one applet shown above, please use "Additions Options..." to upload your translated jar. You might want to filename to ejs_magnetdeflect_fr.jar so that to remind it contain french version translation. Thank you! We can work together to help more users enjoy the fun of physics!