The problem is a character set conflict.
If you're talking about accents from product names/descriptions, then you've probably got your database set to latin1 but you've set your language charset to utf8, or vice-versa. Thus, the data is getting broken during translation. Change the character-set your browser uses to display, and you'll see the problem is resolved ... which confirms that you've got to get the data into your database in the same format that you're trying to output it.
If you're talking about simple display text that's coming from language files, then you've got your language pack set to a different character set than what's being used in the browser to display it. Normally Zen Cart will tell the browser what character set you've selected in your language files. But if you've not set that correctly to match the content, or if you've got customizations that block Zen Cart's normal behavior, then of course that won't work. Again, check your browser's character-set display mode. Normally it should be set on Auto, but if you've set your browser it to only use a certain character set then nothing you do in Zen Cart will fix that.
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