If it is a unicode font, then you can change your theme to have that font and a widely spread unicode font, supporting Hebrew (like arial and arialunicode for Microsoft clients), as default fonts.
Look in /theme/(yourthemename)/styles_fonts.css to check if that is correct.
You also might want to change the default font for the html-editor with the HTML-editor page in the admin block.
Languages
Hebrew Font
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