Sorry if the labels are incorrect, I am using a Spanish version...
Control Panel, Regional settings, Languages (2nd) pane, Settings (top) button, leads you to a new box about Text services and input languages; in your case you should see two entries, one for Serbian and one for English. You need to make sure you are using the same "keyboard layout" for each of your "locale" you are using. I do not know if you'll prefer to use the Qwertz-based (Serbian) as it will give access to Serbian diacritics, or the Qwerty-based "US-international" and heavy blind use of AltGr: this is up to you!
To change the layout for a given language, you need to add the same language with the layout you want, then remove the layout you do not want. Perhaps the actual removing will be delayed to the next boot, such a message would be harmless.
thanks (: but peanut_butters solution not only solved my problem but enrichened the typing experience (as it allows me to map whatever, however) – Invader Zim – 2013-07-07T19:33:26.230