I frequently type both in Hebrew and English. The font I use is Dejavu Sans Mono. This renders Hebrew fonts accurately. However, because Hebrew uses small vowels, I would like to increase the font size of the Hebrew text but keep the English as it is. I have tried various solutions but none have worked for worked for me:
I installed the package unicode-fonts, but this does not seem to have the ability to tweak font sizes.
I followed the instructions in this link How to assign a certain font for each input method/language in Emacs 24? but found no useful solution there.
I use the code below to change input methods:
(define-key 'iso-transl-ctl-x-8-map "f" [?]) ;; Input method and key binding configuration. (setq alternative-input-methods '(("hebrew-biblical-sil" . [?\C-\\]) ("greek-babel" . [?\C-|]))) (setq default-input-method (caar alternative-input-methods)) (defun toggle-alternative-input-method (method &optional arg interactive) (if arg (toggle-input-method arg interactive) (let ((previous-input-method current-input-method)) (when current-input-method (deactivate-input-method)) (unless (and previous-input-method (string= previous-input-method method)) (activate-input-method method))))) (defun reload-alternative-input-methods () (dolist (config alternative-input-methods) (let ((method (car config))) (global-set-key (cdr config) `(lambda (&optional arg interactive) ,(concat "Behaves similar to `toggle-input-method', but uses \"" method "\" instead of `default-input-method'") (interactive "P\np") (toggle-alternative-input-method ,method arg interactive))))));; Input method and key binding configuration. (reload-alternative-input-methods) 
