Je suis anglais. It's not that one way is stronger: it's grammar. If you are wishing for something then you must use 'wish for', 'wish that' or 'wish to'. So for example: "I wish." works and needs no extra words. "I wish for." doesn't work because you don't know what I'm wishing for. "I wish speak French." is incorrect as the statement of wishing isn't joined to the wish. I can correctly say "I wish to speak French" or "I wish for the ability to speak French".